My advice is have no active Wi-Fi connections, go in airplane mode, use Tinfoil to avoid updating firmware and well seek out the necessary files of course! I'm on 5.1.0 and just stay in aeroplane mode going online always runs the risk of a ban. 100% confident if I were to connect online right now I would likely instantly get banned. You just need RajNX, ReiNX or Hekate builds of atmosphere. Not much point for the majority having interest in anything being worked on for the Atmosphere OS as a whole right now, as far as I know.
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Also 100% do that. I NAND backup will save your life. You can possibly update to a higher firmware too without burning fuses. Not sure how but there is a thread somewhere on how to do so though I don't think it's necessary... I think it was 5.X.X the Gamecube adapter support was added so I'm not sure if it works on 4.1.0, might do?
Also, as far as I'm aware you could make a NAND backup with non legit games saves, etc on it and restore between the two as long as they're on the same firmware. I've not tried it but like why wouldn't it be possible. That's if you actually wanted to go online but I really think it's either play it legit, or don't go online at all.