I don't know about single player, but in multiplayer your profile is attached to your cdkey, so if you reinstall with another cdkey from a keygen your profile will become corrupt.
C2D E6750 @ 3.2Ghz, 4GB 800MHz DDR2 4-4-4-12, GeForce GTX 260 c216 OC 896MB, 3.2TB, Windows 7 Ultimate x64
Xbox 360 Elite, PS2 Slim, Xbox