PeterH

Good Morning Eve,
Welcome to the Forum. Do you have experience making molds? You can make a new mold piece but since your greenware piece has already shrunk a little bit I would make a complete new mold instead.
To be on the safe side I would also fire the greenware piece to bisque temp. Then seal it with acrylic paint. 
To simplify your life I would use the remaining mold piece as a starting point and use it in the molding process. Making sure the bisque is sealed and applying three coats of Murphy's Oil soap, to the plaster mold piece, pour a new mold side. The plaster will probably seep down between the mold and the bisque piece but that's alright. After the plaster has set up, 30-40 minutes, open up the mold and clean the seam. Apply three more coats of Murphy's, to the new plaster mold piece, and pour side 2. 
If you were hoping to just drop the greenware piece into the existing plaster mold and pour a new plaster piece you could do that BUT you run the risk of the plaster not cooperating and going places you didn't expect. Then you may be forced to clean new plaster off an old mold. (Been there, done that...not fun.) 
Good Luck

From https://www.cressmfg.com/resources/
... the best I could find is
Basic Kiln Manual, for A,B,C Kilns (366kb)
Kiln diagram C11HT
Can you post a picture of your kiln sitter, or tell us what make† & model it is?
For example, two popular kiln sitters are described in
KilnSitter Operating Manual - Models P and K
Lots of hits if you google Dawson kiln sitter parts
... purely as an example (as it has a nice picture)
https://www.cromartiehobbycraft.co.uk/Catalogue/Ceramic-Kilns-Electric-Kilns-Pottery-Kilns/Kiln-Spares-Kiln-Elements/Dawson-Kiln-Sitter-Spares
... while Skutt has a more comprehensive list of KilnSitter® parts
https://skutt.com/images/KilnSitter-Parts-List.pdf
† And this is a trademark

Handle molds and handle forms (2 ideas) forms are only foam and cheap so you can make your own if you find a consistent shape you like. Press mold a bit pricey but very precise consistent handles can be made easily.
 

Different methods of making handles for mugs https://tinyurl.com/yckrtf6r
Video: https://tinyurl.com/mrnwfa5b

I thought that these were quite neat
 

I thought that these were quite neat
 

Video of the polisher in action
Possibly examples of the OP's work at: https://toaf.ca/gallery/jason-schiedel

Ohm meter has been ordered! I did not get one with a  clamp 
In regard to the element end (the pig tail) I broke while trying to disconnect it from a wire:  what is left is just barely poking out of the hole. It seems if I can stretch it a 1/4 inch or so I could get enough to reattach to the pole (not sure if "pole" is the right word). Since it won't heat up by plugging in, what are my options for attempting to heat it? I don't have a torch, and haven't used on before so not sure this is the best scenario to learn on.  Would a heat gun work? 

One thing that’s useful to know is how your clay develops over a temperature range. It could be that simply firing to a different temperature gives you the color you’re after.
See these links from Tony Hansen’s Digitalfire website:
https://digitalfire.com/picture/baftunycyg

https://digitalfire.com/picture/5m5aJocQuR

I like your thinking but in-situ sounds much more acceptable than live circuit measurement. To have a meter that does both is helpful but for folks without experience in work on live circuits it has increased risk.

my assumption is that you are looking for the amount of sodium in the slip.  the amount of sodium in:  sodium bicarbonate is Na-H-CO3  (molar mass = 84).  sodium carbonate is Na-Na-CO3 (molar mass =106) therefore:  
to get the same amount of sodium you need to 168 grams of baking soda to get the same amount of sodium if you used 106 grams of sodium carbonate. 
In other words you need 1.58 times of sodium bicarb instead of than the amount of sodium carbonate in your slurry recipe. 
All of this is based on the assumption that both the sodium carbonate and the sodium bicarbonate are "dry" solids; that is they have no water attached to the molecule.  Sodium carbonate is more likely to absorb water than baking soda but both can /and will/ pickup water and still be a "dry" solid.  Both are white powders that will absorb water vapor from the air if not stored in a sealed container.   
I have no useful insight if the reason for using sodium carbonate is adjust the pH of a slurry to control suspension of the solids.  I seldom care about suspension as I apply "paste" instead of "slip" on surfaces.  I add the sodium to get the effect of the sodium in the fired surface.  
Regarding @PeterH question: yes. long ago I began using a water spray of sodium carbonate as a means of controlling the fired effect of surfaces.   
I ran out of sodium carbonate but had baking soda in the cupboard and  used it instead; saved a trip to the store and the results were equivalent.  I have been using baking soda more often as it is less damaging to my skin and is available at the grocery store near home.  
A footnote: once the sodium carbonates are dissolved in water they are no longer "sodium carbonates" but are sodium ions and carbonate ions.  the pH is determined by the total collections of ions in the liquid phase.  Soluble ingredients other than the sodium carbonates also must be considered.  
LT

Pure speculation.
As pH meters are so cheap (while presumably still functional) might it be worthwhile monitoring the pH of "unstable" glazes with slightly soluble components. Hoping it gives an early clue about when magnesium additions are required.
e.g. Digital pH Tester Pen Water Pool Hydroponics Drinking LCD Test Pocket Electric
https://tinyurl.com/4pd8wn4m
PS I've no idea what range of pH covers the flocculation process. The buffering effect of the clay could make is very small.

I’m assuming you’re working with lavafleck from Potclays. It’s got a very distinct look to it, and I think by the time you tried to backwards engineer that look, the original might be back in stock. The German suppliers seem to have a lot of options that could work, but shipping may be a factor in trying to substitute.
From a first order standpoint, I think the worst thing you can do is to try and hide a big, time consuming problem to solve from the customer. Especially if the proposed solution looks different than the original item. But you still want to look like a professional. I find if you know there’s going to be an unforeseen problem, but you communicate early and come to them with a couple of possible solutions to choose from, it shows you’re in control of the situation and looking after them.
If it was me, I’d contact Potclays and ask when they anticipate the restock so that I could give an updated timeline if the customer wants to wait for the exact thing they ordered.
Second option is to find a substitute clay that looks similar, show them what that would look like as an alternative, and advise of any changes in order delivery due to material shipping. 
The third option would be to use your existing stock as a slip over another clay body, but you’ll need to do a couple of tests to ensure compatibility. While you’re talking to Potclays about restock times, you could ask them if they’ve got another stoneware in stock with similar shrinkage, especially dry to wet shrinkage, that would work as a good base. You will want to run a test or 2 to make sure this solution works as anticipated.
 

1. Apply underglaze colors.
2. Cover with wax.
3. Draw the fine lines with a needle tool.
4. Let the burrs dry for a while, then brush them off with a stiff brush. If you don't let them dry they'll just smoosh back into the lines.
5. Cover with underglaze (I used black on this piece), making sure it gets into the lines.
6. Let it sit until the underglaze is dry on the surface. This helps to make sure the underglaze is set up in the lines so it's less likely to wipe out.
7. Wipe off all excess underglaze with a fine grained, stiff sponge. A soft, open grained sponge can pull the underglaze out of the lines.

+1 for LinR's suggestion. Article here https://ceramicartsnetwork.org/daily/article/Resist-Inlay-A-Simple-Decorating-Technique
If you want to use a pen,you may find this thread of of interest.
 

+1 for LinR's suggestion. Article here https://ceramicartsnetwork.org/daily/article/Resist-Inlay-A-Simple-Decorating-Technique
If you want to use a pen,you may find this thread of of interest.
 

A manual for a popular kiln-sitter, to give you a flavour of maintenance issues.
http://www.fireright.com/docs/kilnsitter/lt3andk.pdf

I don’t have clay formula recommendations, but you might consider making an engobe or slip of some of your remainder to coat exposed/necessary areas of pots made from another clay.
Test First!!

Certainly temperature has an effect. And I think that a small amount of clay will deflocculate faster than a larger amount would (as it needs fewer sodium ions to do so).
Flambe magic (John Britt's experience of crystal forming in glazes through thermal cycling)
http://ceramicstoday.glazy.org/articles/flambe_magic.html
Deflocculation
https://cawstudiopotters.wordpress.com/deflocculation/

Certainly temperature has an effect. And I think that a small amount of clay will deflocculate faster than a larger amount would (as it needs fewer sodium ions to do so).
Flambe magic (John Britt's experience of crystal forming in glazes through thermal cycling)
http://ceramicstoday.glazy.org/articles/flambe_magic.html
Deflocculation
https://cawstudiopotters.wordpress.com/deflocculation/

That's what I hope the experts will explain. I was just pointing out the use of a specific suspension agent for another glaze very high in  nepheline syenite.

I'll leave it to the experts after mentioning this high nepheline syenite glaze previously posted, which uses a particular suspension agent.
 
 
PS
Glaze additives: https://clayworkssupplies.com/wp-content/uploads/2022/03/Glaze-Suspenders-and-Additives.pdf

That's what I hope the experts will explain. I was just pointing out the use of a specific suspension agent for another glaze very high in  nepheline syenite.

What @PeterH said. Neph sye is a known bad boy in the glaze chem world. It is very high in sodium, which is why it is popular. It is also slightly soluble. Sodium is an alkaline deflocculant, which results in hard panning. The sodium slowly leaches out of the neph sye and at some indeterminate point deflocs the glaze slurry and it hard pans.
Also understand clay is the only material that can be flocculated to create a suspended glaze slurry. Materials such as feldspars or feldspathic materials (neph sye), other minerals such as whiting, etc., or frits do not respond to the alkaline or acidic conditions in the slurry to deflocculate or flocculate, respectively. Only clay responds to the deflocculation/flocculation process. A recipe with little or no clay, such as your recipe with a mere 5% EPK, needs a few additional percent of bentonite (a super clay) upon which to cause flocculation (if needed) by adding a mild acid such as epsom salts. And then after some time, the alkaline sodium leaches out of the neph sye and neutralizes whatever acidity in the slurry has been keeping the clay suspended, and boom, without warning it all falls down. The bentonite is not enough to stop this from happening. Dig it out and remix it with some epsom salts or vinegar to neutralize the excess alkalinity and restore the suspension.
As for the Magma product that folks above recommend, it does not chemically flocculate the slurry. It is an artificial gum additive that mechanically suspends the glaze solids. It is unaffected by the soluble leached sodium from the neph sye. It also has other attributes, so read the cautionary statements on the label. Otherwise, it floats bricks.
 

Apologies, I should have included that but was on my phone. I do know that huge amounts of Neph Sy can change over time solubility, so maybe that is why, but still seems strange it has yet to happen to any other variants much "older" than the one that showed this behavior (and again, happened within an hour). This was a 4k batch all have 3% bentonite to prevent whats happening. I will probably add some epsom salt today (or more bent?) to try and fix it, but I am curious as to the why and why now more than anything.

As for the Hard Panning there was some water on top and the bottom had hardened to the point where a mixer would not budge in it, I had to loosen it up by hand and I finally got it back to normal. Update: Checked it this morning and it was already starting to happen again but not nearly the rate at which I saw yesterday. 

The strangest part of this to me is how it was 100% fine out of storage a few weeks and not until I starting using it did this kick off the issue almost immediatly.
This is the popular micro crystal recipe base "Frosty". 
Nepheline syenite 40.00  
silica 29.00  
zinc oxide 17.00  
whiting 9.50  
EPK 5.00
total base recipe 100.50 
bentonite 3.00 
rutile 2.00