This script will quickly search a hierarchy structure and find all meshes on a particular layer. It will replace the current material with a provided material. Runs in the editor but in order to populate the Transform array, start the game when it needs to be populated or repopulated (see video). Short and simple, but I found it useful. I was using a nested structure for my modular environment pieces and didn't want to mess with the initial fbx materials or set their material manually.
Here's a quick video of it in action: