Custom recipes?

In the mod jar, in assets/ic2/config, there's all the .ini recipe lists that IC2 itself uses. You copy the ones you want to change into a folder called ic2 in the config folder. Each one has an explanation of the format, and with the examples of the real things it's not too hard to work out. Not all the machines currently have them, but a fair number do (including the thermal centrifuge ).

Yes, as IC2 also uses the ini files for adding nearly all of the crafting recipes (the only ones that don't are things like the quantum suit dying recipes). You can modify the machine recipes in the shaped_recipes.ini file, as all the machine recipes are shaped, by using it like you use the machine files.