Lord Revan 57,
Welcome to the Star Wars Knights boards! The official ruling on this can be found on the Forums Rules and Guidelines (
http://www.lucasforums.com/showthread.php?t=169078).
Rule 7 of Holowan Laboratories states:
7. Mods containing assets (models, textures, sounds, etc.) ported from another game are prohibited
It is against Lucasarts policy to port assets from one game to another. Holowan Laboratories does not condone porting of this nature, and moderators will close or delete any thread or posts discussing such mods, even if it is for your own personal use. The exception to this is if the asset in question is present in both KOTOR and TSL. Modders may create from scratch mods that resemble assets from another game.
(That's where the "illegal" part comes in.)