I see you want a special keyword to add a mapflag to all maps. I don't see the need, and by see I'm meaning I'm not seeing you point out a purpose on adding that while the same feature is already available by zones, since in map_zone_db within the 'All' zone you can have
mapflags: ("adjust_skill_damage MG_FIREBOLT 50" )
Tried this but it doesnt work.