Follow the instructions posted in some of the threads here on taking a backup of the internal SD card before trying anything
While yes, a script has been posted that will do a backup without removing the card, nothing has been posted for a restore
So physically open your unit, use a tool (dd under linux or maybe Win32Imager under Windows) to take a full backup of the SD card; restore that image to a brand new card that you will put in your Kobo, and then put the original in a safe place.