Help modifying Unique Battle Music Per Unit patch to work on enemy phase

I want to enable some units to have unique battle music that plays regardless of whether they’re the one initiating combat, which is not an option with the patch included in FEBuilder.

I have no experience with ASM, but in preparation for this question I did figure out how to install the existing patch via buildfile at least, since I assume that will be necessary. Now I’m just stuck on the part where I have to actually understand the code.

Any help would be much appreciated