Only the graphite ones that Loki & AMW use. I wouldn't ever reuse one that's meant for single use. Even if it looked OK, would you want to bet your rocket that it was?

Not typically - and not on a non-research day. The Aerotech phenolic nozzles erode during the burn. It would be interesting to see just how much they open up for the different reloads and burn time - but that's a seperate issue. And, far more measurements than I want to take.

Other cases like Loki, AMW, and research cases use graphite nozzles which does not erode too much. They still do, but have a much longer 'reusable' life. After they open up a bit then they can be cleaned up and used for the next needed size.

There are those who collect AT nozzles and save them for research loads but the graphite is much more dependable.

Yes there are people who have reused single use nozzles some with good results and some with bad. With aerotech nozzles they do erode but if you know the rate and that is what you are looking for then great. Just have to make sure the starting throat size is correct. Now would I recommend it no but it can be done. Problem is it is usually way more work that I was ever willing to put in to get it to work right. Just use a graphite nozzle/

Pretty sure Cliff has done so with very mixed results. In this case, I probably wouldn't do that if I were you.