Is it possible to add custom music to the game?

You can also do it like this:
1. In the Map Properties Tree, find Music and click on "...".


2. Choose any theme for the heroes (in my case, it's Godric).


3. Enter "SomeMusicName.ogg" instead of "Heroes-Godric.ogg". Make sure that the music is in OGG format and you need to put this music into the Music/AdvMap-Heroes folder.


4. PROFIT