Creating New Subarenas
From ASSS Wiki
To create a new arena type ?makearena (arena name). Settings changes made in this arena will now only apply to this arena.
It's a good idea to not be in the target arena when sending the command.
To change the map, change the location of the file in the [General] Section. Or when in the arena you can use ?putmap <mapname.lvl>, the map will be uploaded from your client directory to maps/uploads/ and the arena.conf modified accordingly.