When I first started with clay it was with cone 04 slip. The rules were pretty clear and on the mark. But when some years later I moved into using pugged clay cone 6 for hand building and wanted to use more than one color or type ie: porcelain and stoneware. I was told hat I could only expect failure. What a joke that turned out to be. I always question and try things out for myself unless shown concrete proof. So not only do I mix porcelain and stoneware. I also mix my brands, Bray, Laugna, Immco ect.
I also mix different colors, blacks,browns, reds and the list goes on. Presently I have 7 different colors and 6 different brands in my studio. The only thing I look for is the firing cone and shrinkage rate. Now I am not building any large or heavy pieces but I haven't had any problems in the last 15 years. My advice on taking advice is take it with a grain or shaker of salt. And experiment we all learn alot from sucess and failures both.