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It's entirely possible as long as you have Fred Tetra's KotOR Tool and both games.
Using Kotor Tool, you can extract the original head textures from Kotor1, save them as TGA files, rename them using the same name as the texture you want to replace in TSL, and drop them in your TSL override folder. Make sure you're using the same head model when you do this. For the most part, the Kotor head models are all in TSL as well - they're just re-skinned.
FYI, all of the PC faces are under "ERF's>Texture Packs>swpc_tex_tpa.erf>P" in Kotor Tool for Kotor1 and 2 both.
It may take a bit of experimentation on your part to figure out which ones to replace, but feel free to post if you run into any trouble.
The reason there are no mods of this type available is that it's against the rules of the board (not to mention illegal) to port stuff from one game to another. As long as it's just for personal use (AFAIK) it's OK.
Almost forgot - you can get Kotor Tool here:
http://kotortool.starwarsknights.com/)