Just shave it off, I did..
Doing it for the last two years. Since the transplant procedure has become very common nowadays and my donor area is becoming thin with each passing day, I am thinking to go for it soon.
If your DONOR area is thinning, then you need to be extra cautious - the donor scars may become obvious later on.
Exactly that is not the ideal situation to be in. Especially if you are still also dropping hair up-top and you would maybe 5 years later fill in further from the donor area to the top. You will end up with a scar/bumpy skin that shines through your thin donor area and potential empty spots on top as well.