1) Just download gta sanandreas ultimate editor, i forgot the version but you'll find it here, go: downloads/tools/gtasa ultimate.
2) Open player.img by pressing img tool and find these files:
player_face.txd
player_torso.txd
player_feet,txd
player_legs.txd
When you find player_face.txd - this is the face of CJ, press edit txd then press export - gtaultimate will change the format of .txd to .bmp, and then edit what you want in this file.
remember don't close gtasa ultimate!
If you finish, just press import and you'll replace the default file with your file, then press close editor, press "yes" to save the changes and you have your own CJ!
P.S. if you don't understand tell me and i will upload the screenshoots ok!