*BUMP*
But better late than ever.
Okay, my comrade, first of all, you gotta extract the file ya wanna edit, I.E.: you want to edit Cj, open gta3.img, in the Models directory, with IMGTool (make sure you got 3.0), and search for "Player.txd", now, open TXD Workshop, and open "Player.txd", now, click on "Export", and choose a destination folder, now, you can edit it.
Edited?
Cool, Now, click on Import in TXD Workshop, and select the file ya extracted, Save.
Thats all, If'cha need to know more about it, lemme' know.