Here is a list of all the different commandline commands that exist.
-user This starts the game with a different user name. If not set, game is started with "Default".
-cfg This changes the main config file that is used when starting the game. default is "config/main_init.cfg"
-map This starts the game with a specific map. Default is what is specified in the user settings.
-mapfolder This starts the game with a specific map folder. Default is what is specified in the user settings.
-mappos Sets a specific start pos to be used. Default is what is specified in the user settings.
-workdir Which directory the exe should load in. Can be used to change between engine and main redist