Just to add my experience. I had SX os and was playing “backups” of botw and dk for a few weeks and ran minimal homebrew. I deleted my WiFi connection so it would stay offline. Yesterday I decided to go legit and I proceeded to reset the switch without deleting save data and formatted the memory card. I connected to WiFi and paid for and downloaded the games I was playing and the previous saves loaded right up. So far I have no issues and I am not banned. I even tried playing fortnite and paladins online. All is running smooth, and I hope it stays that way. So, in conclusion I think depending on how you modify your switch a reset may be all that’s needed to go back online.