If you want to mod TBoGT you need to change the files in -
Grand Theft Auto IV Episodes from Liberty City\EFLC\TBoGT
I never changed to Luis skin, but if you want to change the clothes go to
\EFLC\TBoGT\pc\models\cdimages and then open the playerped.img file.
If you use OpenIV, you can add new clothes.
You can use all the GTA IV clothes mods and the GTA IV clothes.
And by the way, the most GTA IV mods working with TBoGT.
You can find the normal GTA IV files in
Grand Theft Auto IV Episodes from Liberty City\EFLC
From there, it's like normal GTA IV modding.