If your going to 'frank' base models I'm ok with that. Raven gives permission to modify their files as mods as long as they stay in JA. So that is perfectly acceptable. The issue with 'franking' is when it involves other peoples models. That's for another discussion though.
Why not just take the trainers clothes (skin) and put them on the jedi model? The only thing you'll lose is the shoulder pad. It will be much easier than going through all the work to pull the heads off and re-rigging the whold model.
heh in fact i already tried that. result is not very good, texture sized for a model does not fit correctly on another. anyway as you say is really much simpler. hope someone has a simple step by step tutorial to make this ! thanks anyway :)