Changing materials on multiple objects with a single GUI button

I am new to unity and scripting and am working on a project with multiple light maps baked out of 3ds max and plugged into lightmapped materials. I am trying to find a way to switch between materials with and without the lightmaps to simulate the light turning on and off. I have gotten it to control switching the material of a single object with a single GUI button (through some searching and a tutorial) but I am struggling to find a way to also make the same GUI button control switching materials of several other objects in the scene. Any help would be much appreciated.