If you used EmuMMC only then yes, you can just format the SD card. You should probably also reset SysMMC so you don't hand over anything from you (purchased games, Nintendo account)
However if you used SysMMC for CFW then SysMMC is probably dirty...
I have a xaw-1002 switch and I installed custom firmware an SD card to hack it. I am planning on selling it and want to revert into a stock switch. Can I just remove the SD card, format the card and the switch, and everything is stock? I do not...
You ever try soaper powder/qauludes? I did once and like a dumbass drank beer on top of taking, I woke up laying in my backyard in the pouring rain, it knocked me out. I have not seen it around in many many years.