I'm not at my usual PC so cannon check the firmware myself. If you can use a hex editor then open the firmware and search for the commands rrgn (copy), xrgn (overwrite) and ergn (erase). Search also as (for example) r.r.g.n where "." is a wildcard character. If the commands are in the firmware then it's maybe possible to use ergn to erase the detail map. The problem I foresee is that SD text commands need to be initiated by Ldr.bin [boot.bin] in 'normal' Garmin-OS devices and I have no idea how to extract the appropriate BIN file from an *.update or *rgn Linux firmware file.