Yes. You can sand the clear coat and recoat. It actually depends on how much damage you have done to the surface. If it’s minor scratches and nicks, then you can sand it down and recoat. If it’s major scratches, then sand it down and start over. If you have any major scratches, it’s not worth it to do the entire vehicle. One thing to consider is that you are going to have to either use a polisher or machine to do the sanding, or do it by hand. Professional detailers most likely use a polisher.