Overlay Materials?

Is there a way to add transparent overlay materials without editing the original material?
This was possible in Unreal Engine 2 (UT2004) via Unrealscript.
I would love this feature in order to add cracking effects to my object for all materials applied to it.

Bump, I would like to know this as well in order to make Skyrim-Like shaders when the enemy is poisoned or burning ! =D

You could apply a decal with a dynamic material instance possibly, but thats the only way I am aware without changing the original material.