Short explanation of what it does. 

Whenever you want to call a shader, you can call a function in this script with a unity event to call that shader and put it over the already existing shader. You can also say what shader you want to call to make this script more versatile. 

How it works 

All this does is look through all the Gameobjects in the list of Gameobjects, for Gameobjects that should have the material on top of it for that specific material, by using its name. After that it adds all those materials to a list so you can change them. 

After saving the materials that need to be changed. This function goes through that list and changes the materials, so the shader will be put on top of the already existing shader.