Yes, it's possible in number of ways.
Playing quickmatch allows you to set up one-map matches with various settings provided in the menu. You can also choose Advanced there, which gets you to start matches with more options via start_game and other XML commands. An example is provided with the game, man_vs_world.xml, at media\packages\vanilla\custom_matches. More info on commands can be found at
http://runningwithrifles.gamepedia.com/ ... _interface.
If scripting is more your thing, you could take a look at
viewtopic.php?f=7&t=2203 and change anything about the way campaigns work, or create custom campaigns based on the existing campaign.
If the question was more about online and setting up servers in specific ways, the scripts would be the place where to start looking. As pre-made modes RWR offers Dominance (also known as Classic, PvP), Deathmatch, Invasion (cooperative, much like single player campaign), Minimodes (mainly stage setups for Team deathmatch, King of the hill and Teddy hunt), Team elimination and Teddy hunt.