After downloading ALOT of avatar appearance modifying add-ons (faces, decals), I couldn't help but think that people with 3-D modeling stuff could make new hats, shoulders, body pieces, etc. It just sounds like something someone could make more of. So, to find this out myself, I did some exploring in the base folder. And I found the files that have the hats & such. So me (having never modded) feel that making some kind of 3-D model with some fancy script and putting it in there would do the trick :D. Thanks for your time, five cookies for anyone who figures it out.
Ps: If it works, I want kitty ears :3