LEGO Racers mod needed

Hi there. I'm looking for someone who can modify opponents in LEGO Racers 1. This includes, switching out small opponents to boss racers. I understand that there are 3 different elements that need to be changed: the characters, cars and the voice. Although there are only certain characters we're looking to change on certain circuits.
Here's a link to the game in questions: this was a modded version created by CaptainGolem -- https://youtu.be/r8Wtf_0ynH8