Ok, i've made some progress but so far only helps me, not you for sure yet. I've made Pacific Basemap into an RGN, found the region number 33 in a hex editor, changed it to 03 and flashed it to my US 2720 which had Americas Basemap on board. I now have the Pacific Basemap in it's place. So far so good.

But when i change the region number to 49 in the rgn file of a small detail map, Rarotonga, update.exe either reports that the device isn't responding or immediately finishes as successfully flashed but my original primary detail map's still there. I've since loaded it successfully as the primary map using the WebUpdater command line method no problem. But my 2720 is healthy, so WebUpdater is unlikely to work for you if invoked by command line when it can't see the unit using the GUI. If you want to try it, i'll upload the kit for Rarotonga, it's the smallest map around, only one tiny tile 63,469 bytes. The whole image is only 86,016 bytes [84 KiB] and it flashes in a few seconds. If it does work for you it'll clear rgn49 which should un-brick the device. Something to try while we wait for the Cavalry.

This is uncharted waters for me and it seems the Cold War has restarted, no help forthcoming from the East. ..... Wait! .... Did i hear hoof-beats?