Codes
You can enter any one of these while creating a license plate. Once finished inputing the code name make sure the okay button is highlighted first then press L1 + R1 + X.

Become a biker	HAWG
Become a blind, mado-sachoism, donkey smoking a cigarette	JASS
Become a butcher that is asian	PHAM
Become a commando	M1K3
Become a famous boxer	BRUZ
Become a female punk	B00B
Become a gangster	TFAN
Become a lady who has a tatoo everywhere	TATS
Become a male punk	MNKY
Become a nasty corpse	J1MM
Become a pimp	PIMP
Become a police officer in a higher position	FATT
Become a S.W.A.T. team member	5WAT
Become a street bum	B00Z
Become a working asian	HARA
Become an asian that likes gambling	MRFU
Become Johnson the police officer	FUZZ
Become Lola	LOLA
Become your female boss	B1G1
Become your partner	ROSA
Become your partner but wearing lingerie instead	HURT_M3

Cheats
Enter these on the map screen and not during gameplay:

Unlock All Impound Garage Cars	Up, Right, Down, Left, Up, X
Unlocks Snoop Dogg	R1 ,L1, Up, Right, Left, Down, L3, R3, X, Square, Circle, Triangle
All Driving Upgrades Unlocked	Left, Right, Left, Right, X
All Fighting Moves Unlocked	Up, Down, Up, Down, X
All Gunplay Skills Unlocked	Right, Left, Right, Left, X
Bigger Car (must be in car before you enter it on the pause menu)	Down, Down, Down, X
Boost	Up, X, X, X
Impound Garage Cars Unlocked	Up, Right, Down, Left, Up, X
Show's Nick Kang's Current Location	X, Circle, Square, Triangle
Smaller Car	Up, Up, Up, X