Many reasons?
loading 12 textures in memory is a safe way of jumping off to a really bad start. The MS cost of rendering this one item will be at least 12 times as much as any other. Thats also assuming that the number of drawcalls is 1 and not 12. Hard to say because it depends on the material.
if statements arent blocked (Meaning they evaluate no matter what is true or false) however, so they always completely calculate making the number of instructions of the material a lot.
On top of it, I would have to assume you are doing at least some basic blending, which doubles the instructions needed for every texture. And the question remains. What for? Do you really need to change this in editor so much? The real answer is likely No. You just use different meshes, decals, anything that’s cheaper.