Gangster

Unlimited lives:
Load or reset the game, then execute the following BASIC command before running or restarting the program.
POKE 5989,58

Unlimited lives (alternate):
Load or reset the game, then execute the following BASIC command before running or restarting the program.
POKE 53264,123

Unlimited lives (alternate):
Load or reset the game, then execute the following BASIC command before running or restarting the program.
POKE 5374,44

No opponents:
Load or reset the game, then execute the following BASIC command before running or restarting the program.
POKE 53264,126

Cheat mode:
Load or reset the game, then execute the following BASIC commands before running or restarting the program.
POKE 53264,126
POKE 3574,44
POKE 5989,58