For NV Backup: Open the *.gcd file in RGN_Tool. In the first section is the boot.bin, click 'Save' on the right and save it as 'Ldr.bin' in the folder 0723.

For flashing the firmware: You can name the rgn file as 072301000300.rgn if using the nuvi 5xx boot.bin with the zumo 220 fw_all.bin [safest way]. See new point 5 in Post #40.