I want to alter a creature mesh so that it emits light while alive and stops emitting when it dies. I'm not talking about adding a glow map or effect shader. I want to actually make it light up the surrounding area like a torch, but with a different color.

I know about http://tesnexus.com/downloads/file.php?id=29735 by Arkngt, but that uses scripts to create those effects in game. I'm looking for a way to modify the .nif itself to accomplish this. Anybody know how?

Not possible without a script. Only items in the 'light' category and the light spell effect can emit light.

So even if I attach a NiAmbientLight effect to the root node it won't emit anything? Well, that shoots one of my ideas down.