Hacking Update sx os sysnand to atmosphere

[ubas]

Hi guys.
I Bought a switch with fw 8.xx with sx os. Now i have not the mmc and have not a nand backup. I think that last owner run sx os on sysnand (because there are some games on it).
I wonna know if is possible update to the last fw without go in ban, and run atmosphere. I believed i can just update from ofw but i think i could be banned when i log in with a dirty sysnand...
Thanks for help!