I had the same issue when i was stationed in MD. Most local police are not aware that when you are in active duty status, you do not have to change your plates, license, registration, etc. to the current state as long as you claim another state as your home residence. Even if you dont have a residence there currently.
I was told i had 60 days from when i moved to MD to change all my stuff over by a trooper that pulled me over. Then i got a ticket by the local water patrol for having MI regs and he has seen me on the water for over a year with them. Went to court, judge threw it out because i was active duty military. Youd be surprised who doesnt know about that. I was a MP and we had DOD police on base and they were trying to ticket all the permanent party for not changing their plates and so on.
I would get the fire extinguisher for $12 at walmart and if you get stopped again and get told you have to change to NC regs. Explain that you are active duty and are allowed to keep your home states registrations. Be polite though. Chances are, the officer isnt aware of that or wasnt aware that you were active duty military.