Yes. You can make different folders for music depending on the situation:
My Documents/My Games/Spring/sounds/music/war/
My Documents/My Games/Spring/sounds/music/peace/
Music has to be in the OGG format.
The peace tracks are the ones that play at the beginning, switching to the war tracks once combat starts happening. There are also victory and defeat but those only play after game over so there's not much point in customisation.