How can I downgrade my N3DS to 9.2 sysNAND and 10.5 emuNAND and keep currently installed software?

That's basically it.
I know how to downgrade firmwares, but how do I keep all my files.
I did it on a 3DS with no data on, so I don't know if it deletes anything. If so, how can I restore a backup or something?