Q: Is it possible to enable the multiplayer buy menu to skirmish?
Yes, but only if you play via LAN or Internet. Move your skirmish map to multi map folder, rename the 0.mi into combat.mi and place some spawnpoints for the players (see multiplayer combat.mi files as reference). After that disable all skirmish menus by holding ctrl and clicking on the menu triggers in the editor. You will need to change the win condition and flag capture condition to make them function with the spawned units as they don't carry a tag. The game automatically assigns unused players to multiplayer users. 0-3 player is assigned by the skirmish, so the next one will be the host.
http://digitalmindsoft.eu/forums/sho...official-guide