Yes, you can do sections or half. You need to get a map or even look at Google maps. You just need to choose your priorities. There are lots of NC500 websites, books and advice. There's even specific NC500 maps. Check some of those out. The whole area is beautiful, designated route or not. To do a smaller section you will probably end up doing a loop out and back.
One thing: Make sure you go watch some of the YouTube videos on how to properly drive and pass on the single track roads. Hint: the wide spots aren't for parking, they're for passing.
If you have less time you need to choose the sections that are more adjacent to the rest of your itinerary. If you're going to be in Inverness, going up the east coast is the easiest rather than crossing the whole country to do a day trip to the NW corner. If you're on Skye, then doing a section on the west might make more sense. The famous hairpin turn hill route is on the west, north of Skye. If driving that is the main goal then you should site yourself appropriately. If beautiful coast, places to stop and enjoy are more your priority, you will have more flexibility on how to put this together.
Also, there aren't a lot of spots to turn around easily and some attraction signs are small or very close to the turn off-and there may be only one entrance-so pay attention if there are sites you are wanting to stop and explore.
