i replace them by the original awp u have to go to C:\Program Files (x86)\Steam\SteamApps\common\Counter-Strike Global Offensive\csgo\materials\models\weapons. there are 2 folders v_models and w_models (v stands for viewmodels and w for worldmodels worldmodels are lower res). u have to convert ur .tga to 512x512pixels for the w_models and v_models can stay the same. (since that is the texture u created on the original size. then convert that tga to vtf with vtfedit. and put them in the folder for what weapon u have created mine was awp so snip_awp. Change ur file name to the exact number of characters of the original one. (the original one was called awp so i named mine awb). once u have done that u have to make a copy of pak01_dir and rename the copy pak01_dir_bckup or something. Now edit the original pak01_dir with notepad++ and search for ur weapon, in my case awp. then change these lines so the game knows wich texture to use instead.

Line 11345: "$basetexture" "models\weapons\w_models\w_snip_awp\awp"
Line 12594: "$basetexture" "models\weapons\v_models\snip_awp\awp"

now save the file and enjoy ur skin ingame!

i hope i awnsered ur questions!