The music integration is made with a middleware audio engine, and for every zone you are, there is like 8 tracks for what I recall that are playing simultenaously.
This is a key element for game music, so the music can change from "idle theme" to "battletheme" smoothly, for example.
There is actually no point to spend ressources for a feature like this, I mean in a pragmatic point of view. It surely is a good idea but costly.

Having your idea in game mean :
- Converting the ~4 tracks into a single one. This imply studio mixing, because multi track for game implementation mixing is different that "classic" studio mixing.
- implement these news tracks to the game
- Sound Designers should implement new condition to make the "normal" music behavior being bypassed by your feature, "on the go" (on a clic from user)
- Find the better solution to not impact your performance. Because, this kind of feature for being responsive means that every piece of music is loaded, everytime.