You’d have to decompile each model, then rerig them to the new hands (mp ones, too), then recompile them yourself and hope it works properly, and the animations are compatible. I can already think of a few models that would need a few modifications, too, because the new animations show the side of the model you usually wouldn’t see, meaning there are missing polies on the old ones.
Mm, I think you’d likely still have to recompile some (esp. if you want them compatible with MP). Also if they’ve changed their file structure for any the weapons, you’d have to change it to the old paths in the weapons’ script files, or modify the path in the QC. And still hope it works properly.
Different hand rigs, code and sound, and world models are different.
Oh, have fun with that.