If you haven’t yet familiarized yourself with modding Persona 5, check out this guide first! This is a more advanced follow-up to the EBOOT patching and BGM editing guides, so read those first as well.
Copying and Renaming ACB/AWB
You may have noticed that the DLC tracks that play when the protagonist is wearing a DLC outfit are not in bgm.awb, but each have their own ACB/AWB pair. Each includes 2 ADX tracks, a battle theme and a victory theme. Maybe you also noticed that patch.yml has a Randomized Battle music patch, which shuffles all of the DLC tracks (in addition to the main battle theme) and randomly picks one at the start of each encounter.
You can customize this even further by adding your own music tracks to the game, following the same format as the DLC tracks.
You can theoretically add an infinite number of custom tracks by copying, renaming and editing the contents of each ACB/AWB pair.