we don't actually edit the map at all. the developer mode in the mod allows us to add scripts to the mod to add support for the maps that we want to use. nothing is physically added by us or changed on the map. the mod just "spawns" the objects that we want on the map. and as such nothing is added and therefore nothing needs to be taken out and as such no need to download the same map twice. if you got the map from a dm, freezetag or mixer rotation, that's the same one we use.
that is why we are able to use the maps in the >xi< rotation as well as the maps specifically designed for the mod.
in order to get a map designed specifically for the mod to run on a normal server, it would have to have dm, tdm, domination etc. spawn points embedded into the map. each new custom map would have to be checked and tested for compatibility in that regard.
i hope this has answered your question.