If you want to use a single map for all game modes, add the game mode as part of the command line.
If you setup the alias system, you can shorten that to:
By alias system, I mean the GameModeClassAlias list in your DefaultEngine.ini:
If you need to have specific game mode related changes to a map for it to work correctly, I recommend using the permanent map as the gamemode map and adding the map geometry and so on as a submap.
Then you can use the prefix system to define the game mode:
We use the latter method, as it quickly became difficult to contain so many different game mode changes in a single map