Why wouldn't 'rcon map' work? You're using reborn, right? So you can use the 'stuffsrv' command to access the server command line:
stuffsrv "map dm/mohdm7";
The old way would be to use 'leveltransition' or 'bsptransition', the difference being that 'bsptransition' retains the players' loadout (and even health in single player) while 'leveltransition' puts everyone in spectator mode again.
local.gametype = getcvar "g_gametype";
setcvar "g_gametype" "0";
setcvar "nextmap" "dm/mohdm7";
leveltransition nextmap;
setcvar "g_gametype" local.gametype;
Interestingly, if the 'nextmap' cvar is empty, it will simply change to the next map in the map rotation. If the current map isn't part of the rotation, it switches to the first map. Also, if the 'nextmap' cvar points to the current map, the current map is not reloaded, it is simply restarted.