Unlocks 2 secret characters: Drumstick and T.T.
Also unlocks all the magic/cheat codes and turns on "Select same player" and "Two player adventure" by default:
Use a patching utility such as Lunar IPS to patch your rom.
Database match: Diddy Kong Racing (USA) (En,Fr) (Rev 1)
Database: No-Intro: Nintendo 64 (v. 20210220-053642)
File/ROM SHA-1: 6D96743D46F8C0CD0EDB0EC5600B003C89B93755
File/ROM CRC32: 5ACCA298