FreeGameDev

If you ever do more weapons personalized to karts, some ideas I had to replace bowling balls are a coconut for Suzanne, a snowball for Tux and Mr. Iceblock, a marble (the glass kind with swirls of color through it), keep the bowling ball for someone, maybe have a baseball and a pool 8 ball.

Many of these are add-ons though. Of course you could have models in the kart export...

Bad idea, only Nolok should have personalized weapons (or maybe one more evil guy)

While this can seem fun, it's a lot of asset management, I don't think the work this would require is justified

It's a very good idea ^^ Perhaps, for me moment, put any objects in different main characters : Nolok, Gnu, Suzanne and Tux.