Actually you cant get unbanned. You need a new Sync ID and for that you need a Save File thats has never been online. If you happen to have one first you need to UnRegister the game from your GL Account then wait till Tuesday(The day of the maintenance) for the game to be fully unregistered from your account. Then load that save file to your game, create a new Sync ID, then register the game and you'll get "unbanned". If you dont wanna wait load the save file to the opposite game(If you have Sun registered then do it with Moon) you have registered on your GL Account.
In other words if you get banned that save file is lost unless someone find a real way to unban your save file.
I was assuming there was a jksm backup, (I've made a few at critical points for various reasons) but there were no mentions of specifics. That seemed logical to me.
Although, if we pretend that isn't the case, maybe the other route is as you've said. Throw in some PKHex for fun.