Hey javlien, you can do it for sure... Indeed, you can use anything to convert to anything.
AOBR termies to chaos termies, Chaos Termies to space wolves termies, Regular Termies to orkz Mega Armoured Nobs ^^
The hobby is just about it: taking wheatever you want to give your models the apearance you want
The only limitation here, is that
GW events dont accept non
GW models, but you are ok with that, as
AOBR is a
GW product
As how you coild make that conversion: i depends a lot on what you want:
AOBR termies comes with storm bolter and power fist (a plain, bare power fist).
Chaos termies use a twin-linked bolter, so you have the first thing to convert (remove the bolter and replace it with a pair of bolter glued together?)
Those powerfists can gain some chaos symbols too, and some "spike bitz" can greatly increase the feel of it... skulls, chains, spikes... that is up to you, and what you have available...
One good thing i can tell you: take some photos around to use as inspiration, use some green stuff if you have the skill, try to make their armors look more barouque and less clean... All that is part of the converionist experience, and it is a lot of fun...
I hope to have helped... good look on your converions, and dont forget the pics ^^