Shouldn't be too hard, once you find out the mechanics behind it. If there were battle summons it would be easy to figure out how to bring in the transformation, then find a trigger that would just remove the old model. But without them you need to find it out from scratch which is a headache.
I look forward to Stardock or a modder putting this in so we can play around with it, i'm thinking Lycan...
Yeah a Lycan faction would be great! 
