Do not attempt to modify the XML manually. Not that a know of. You can use gconftool-2 to modify settings individually. Use "gconftool-2 --help" or google gconftool-2 for help on how to use gconftool-2. Otherwise, just use Maemo Mapper itself to edit the settings...
gconftool-2 --dump "/apps/maemo/maemo-mapper" > /media/mmc1/MMMaps/testdump
gconftool-2 --load=/media/mmc1/MMMaps/testdump