To set a default playlist, type
[caves] for the caves playlist
[plains] for the plains playlist
[title] for just the title track
To set just one song, you can find the song file-names in "music".
Type your desired song/playlist into the text box on the first tab in mapmaker. It has the text "custom music" above it.
Type music as the file name. ex: "plains2.mp3"
Playlists can't seem to make up their minds if the brackets [...] are needed.