To unlock this achievement, you will need to do a few things:
- At least $50,000 in earnings to purchase customizations
- To have won a GP with all 4 of a characters cars
- To have won a GP with the car you want to customize
- Complete 20 drifts in a single race or 300 total drifts with the car you are going to customize
- Boost 10 times in a single race or 100 total boosts with the car you are going to customize
Once you have done these things, go to the Raceshop, select the car you want to customize and change each item to a different options (meaning not 1 of x). Make sure to not miss the Palette.
After doing this, complete any race (I did an Arcade race) with the customized car and the achievement should pop.