Hi,
that's some good questions, finally :)
Those vehicles are not meant to be file-swapped anymore, now it would be more comfortable to start using unlocked slots (available from ALPHA 4) or new slots (in ALPHA 5+). As unlocked slots and new ones always have dedicated rim set and files.
But indeed the game originally does not support a different rim set (nor rim files) for any of Saleen Mustangs, they all share the same one.
There's a database fix, the patch can provide dedicated rim set to each model (S281_F_02, _03 ....) for the sake of customization.
I will add this for future version, it might also apply to other 'duplicate' models (SLK55, Alfa GT, 350Z....)
Concerning character animation, I have not the knowledge in TDU animation files (does anyone ever has ?). So don't expect too much for now, sorry ;)