mode after making a backup of your save!
Not all combinations are good for every situation and most of them will produce undesirable results. There are a few good ones though.
Print the current game mode.
Enter an interactive commandline menu where you can set the game mode.
You are in fort game mode, managing your fortress and paused.
You switch to the arena game mode, assume control of a creature and then
switch to adventure game mode.
You just lost a fortress and gained an adventurer.
You are in fort game mode, managing your fortress and paused at the Esc menu.
You switch to the adventure game mode, assume control of a creature, then save or retire.
You just created a returnable mountain home and gained an adventurer.