Not a need to do it by flashing to a region for the file system. The commands for copy and copydir can be used to write/overwrite files & folders in the file system, even the complete directory. See: [Only registered and activated users can see links. ].

To use WedUpdater, MapUpdater or GarminExpress, as you said just copy the unit's GarminDevice.xml to a Garmin folder on a clean USB drive or media card of minimum 2GB size and the programs will see it as the actual nuvi. You can replace any Voice, Vehicle, Help, Text, Keyboard files etc also TZ and official detail maps that way, but you'll need to get a basemap separately: [Only registered and activated users can see links. ].