Per the navigation owners manual (P. 177) you are allowed to make one backup copy. Using the Navteq software, "Naviextras Toolbox" you can make a backup, and then restore the backup. Question is, can you restore to a different SD card? I would assume so, in the event the original was lost or destroyed.
Can you swap the OEM card into a different unit (car)?
https://subaru-na.naviextras.com/sho...x&topic=Backup