Every Setting pairs one levelName with one gameMode number (same mode ids as Lua mm_defaultGameplay: 3 capture base, 4 control, 9 sentinel, 10 king of hill, 11 bomb base, 12 TDM, 13 GTDM). forbiddenOnLive 0 shows it, 1 hides it from the live lobby (used for raids 7 and brawls 21/26-31). 
<LobbySettings>
  <Setting levelName="s1338_devilsjaw" gameMode="3" forbiddenOnLive="0" />
  <Setting levelName="football" gameMode="21" forbiddenOnLive="1" />
  <Setting levelName="paper_airplanes" gameMode="26" forbiddenOnLive="1" />
</LobbySettings>
To allow a custom-lobby mode on a map, copy a 0 line with your levelName and mode. Never list a _ow open-space level here; the lobby cannot host travel sectors as battles.
Additional Notes: 

Mode ids match Lua mm_defaultGameplay list.

Comments

2 + 16 =
Solve this simple math problem and enter the result. E.g. for 1+3, enter 4.