Late entrants still welcome, just reach out to me on discord or follow along on twitch and shout out in the live chat -> https://www.twitch.tv/mm_openra
Yes, you can define it with the parameter Server.Map https://github.com/OpenRA/OpenRA/blob/bleed/launch-dedicated.sh#L20
Needs to be set to a "map hash" though which you have to calculate with Utility https://github.com/OpenRA/OpenRA/wiki/Utility#list-of-commands -> --map-hash