It'd be nice to have the option to change music tracks mid-round, as hearing the same song repeat endlessly until you lose can get monotonous during long marathon rounds.

The simplest implementation would be just "rotate music mid-game: yes/no" and then if yes, randomly select a new track when the current song ends. This alone would be great.

Just spitballing some additional ideas for options:

• Rotate music: [song playthroughs / levels / off] (have the song repeat a bit before changing, or change it based on levels)
• Rotation frequency: # (defines how many playthroughs or levels before the song changes)
• Track order: [random / sequential]
• Rotate background image on music change: yes / no
• Rotate block colors on music change: yes / no

The last one would require a list of color palettes defined in the theme. The backgrounds and colors could rotate sequentially or randomly based on the sequential/random music, or they could each get their own option.