While doing some research for my upcoming runs I came across this site https://gamefaqs.gamespot.com/gba/932086-cars/cheats.

I tested it out and they all seem to work aswell as changing your name to cheater. There is currently no rule against them in any category while the unlock all characters cheat makes all previous runs obsolete thanks to the speed of chick. I would suggest either allowing the cheats and making a no cheat code category or only allowing it in a new cheat code category.

The other interesting cheat code is the one for a secret radiator cap circuit which would be an interesting addition to the all races%