It's possible to add in 'music' mixed with the ambience track as I played around with it a bit. But you can only put in two pieces of ~3 mins of music due to the day and night cycles.
Daytime: 3mins 30s
Nighttime: 3mins 15s
Also the first day cycle that the match opens on is short.
But in any case this leads to a lot of repetition in the 'music' so I lost faith in it. Too bad as I had wrote over 7 mins of ambient orchestral cues for Running with Trench Foot; I may just upload them to my soundcloud for fun. I had a vision to have a large variety of day and night cues, which would play in a random order each day and night; to create a diverse musical experience that would never 'repeat.' However this is not currently possible, and I am not an RWR developer, so I abandoned my vision for Trench Foot to have a soundtrack.
Edit: have a listen if you want. First half of the track is cues for daytime, second half for nighttime. I was going to write even more cues (and was looking forward to it), but as I said the lack of a usable music system made me lose interest.
https://soundcloud.com/karl-feuerstake/ ... -ambiences