When going back to the US 4.20 firmware (from SG/Mal 2.30), can I just copy the US 4.20 GUPDATE.GCD in the .System directory of my US Nuvi 3790T and let the unit update it? No need to make a .RGN file when re-flashing to original US firmware?

If I simply do that (use GUPDATE.GCD), will boot.bin, fw1_resource.bin, and fw_all.bin be back to their original state (US 4.20) again?