Currently the mod has set layers for the pizza. Is it possible to open up the ingredient list to allow more ingredients in each layer, whether through a config file or thru a datapack? This feature would be really nice to have and solves the problem of asking for specific types of pizza.

Of course it's possible by adding items to special tags, each layer is linked to tag.

you can check them here: https://github.com/Tiviacz1337/PizzaCraft/tree/1.19.2/src/main/resources/data/pizzacraft/tags/items/ingredients