Honestly as long as you don't have the shinies starters before you beat the game and don't go into raids/online with them you are safe. I'd wait like a week or so then you are fine with that but still a risk. Any cheated pkm is a risk to a potential ban but it's not as crazy as people like to make it out to be. My friend been sending me pkm on his CFW switch ever since pokemon let's go and he's still not banned and he sells them on ebay too. As long as you don't be too obvious people can't tell honestly. I.E. don't bring in pkm that aren't in the game online battles and you are usually safe. But the best thing to do is just have same profile on your CFW + Legit switch and just switch the save data to the legit one.