I can’t find any rhyme or reason as to why textures won’t show up in the build, despite having no problem in the Editor. Any ideas?
The issue seems to be that it’s okay to change shaders in the Editor, but you need to actually change materials in the Player to get consistent results??
When you say they don’t show up, do you mean they don’t appear on the objects they’ve been applied to or that you can’t find them with Resources.Load, etc?
I didn’t try Resources.Load. I just created an array of shaders, and set material.shader to be something else in that array upon a mouse click. It makes sense that this wouldn’t work, because the properties of the shader have not been explicitly defined, but why does it sometimes work in the Player, and always work in the Editor? That’s not providing me with good feedback about how to go about things.
Sometimes there are unavoidable but subtle differences between the Editor and a built player. Setting a shader is orthogonal to setting a texture or a material and I agree that the behavior should be as identical as possible in all cases. It sounds like you’re aware that you’re using a slightly unconventional approach. In your situation I would set up an array of materials instead of shaders, swap out the material, then explicitly set the material properties to use the specific texture you want to use.
Of course, if you can create an isolated case of the problem/inconsistency in a minimal project folder, please submit it to us and we’ll put it in the pipe!
I wasn’t sure, actually. What I do know is that it’s less work and clutter to not have to make a material for every shader, if you don’t need to reuse shaders! 
Case 298030 submitted!