My exact procedure was as follows, all on an old 3DS XL (games and NNID were installed, I did not unlink the NNID before the procedure):
Made a full SD card backup
Downgraded from 10.3 to 9.2
Used emunand9 to dump the sysNAND
Used emunand9 to format the emuNAND partition on my SD card using...
I've done this twice now with systems that had games and NNIDs already on them. Everything works well until you unlink the nands. After formatting the sysNAND, online services that require a login to a NNID stop working on the emuNAND. You're still able to update games and (I believe) play...