There is no "SpongeBob mode" in Grand Theft Auto: San Andreas for PS2. This appears to be a misunderstanding or confusion with fan-made modifications.
If you're looking for legitimate cheat codes, the game includes dozens for weapons, vehicles, weather, wanted level, and gameplay modifiers. These are entered via button combinations during gameplay. Reliable lists are available on sites like GameFAQs or IGN.
For the authentic San Andreas experience, play the game as Rockstar designed it—the cheat system alone offers plenty of chaotic fun.