I'm not nearly as knowledgeable as some of the other people here but I'll try to help.
Can it be done? Yes. You candy will be much darker though. You'll have to do everything. On motorcycles, it's a little easier to spot in kandy to fill in the lighter areas. On cars, the panels are much bigger...and flatter so you see everything. And if you use a light colored base and kandy, mottling or striping is easier to see if there is a problem. The cinder red base is pretty stuff. I think it looks good with just clear over it.
Anyway, I would scuff the entire panel (or car) with 600 grit to give the new kandy something to grab onto. Perhaps you'll want to shoot it in a different overlapping direction??? You won't be able to just do the hood or just that panel. 2 coats of kandy will significantly darken the panel where it wont match the rest of the car.
Sometimes, the easiest way of doing it is just starting over. I hope that helps.
