My truck still has the original paint,most of the truck is still in great shape. But the roof is badly faded and the hood is is starting to do the same. Can these two spots be repainted without doing the rest of the truck

 

Of course they can, you can do anything you want. But I suspect the hood will look like it's
been freshly painted (as will the roof but it'll be harder to discern that). Have you tried
polishing compound (a less abrasive version of rubbing compound)?