Here is a ROM hack which changes all the tracks in the game to new ones! Also Koopa has been replaced by Toad and the original Toad is replaced by Wario.
Super Mario Kart (Japan) (Rev 0A) - NOINTRO
CRC32: C8002453
MD5: F7AFA112D7EC1D532636703E4B02700A
SHA-1: CBB853BF911255C1D8EB27CD34FC7855A0DDA218
SHA-256: C04F517C2675D7A8F3498D958F097443DFAA0E66606C69C59B58A915B3454973