Maybe this is something that only valve can enable or it could be done by an expert modeller, but I'm pretty sure it needs both codes and models.
I know I sound like a nag but Team Fortress Classic has a basic version, and Team Fortress 2 is going to have an advanced version, but I just like things to be more realistic gameplay wise.
If possible I would like to make it so that you wouldn't have any changes to gameplay i.e. can't join server: your models differ.
I know this sounds kind of ridiculous but I'm not gonna cry over it or anything. It would be really appreciated, and thanks for your time.

Yeah, it would probably have to be done by Valve.

Yep, would be cool. Some of Jed's player models for 1.3 had moving mouths, (If I recall correctly.)

EDIT

Yeah, they did:
http://www.wunderboy.org/playermodels.php