as has been said a couplke of times.. use SX OS and create emuNAND - it will make an exact copy of your CURRENT NAND - saves games, settings, everything (just uninstall any themes you have as they may not work with SX OS 2.7.1, if your current firmware is 8.0.1!)
then if you want to go online you need to restore the very first NAND backup you made.. which may not work if say your original NAND backup was firmware 4.something and you have upgraded to firmware 7.0.1 (the fuse counts will be different and not work).
You can only DOWNGRADE to the lowest firmware which supports the number of fuses you've burned.
If you have NEVER upgraded your firmware then restore the NAND backup and it will overwrite all logfiles which may cause you to be banned.
If you cannot go back to the first NAND backup then there is no guarantee your switch will not be banned when you go online, due to system logs containign details of NSPs etc you have installed.