DeathChaos25 showed in Twitter that it's possible to add 2 more Music Tracks playing on Battles (At least when Ambushing the Enemy) and I thought, can this be applied to the Costumes Music?
While I don't know the answer, I actually made a list of the Tracks I would add per costume (At least for the Persona games, I don't know much about the Other SMT games music) and in addition to that, change the music for the Sub-Boss and Boss Battles for the Costumes as well (When it plays Keeper of Lust and Blooming Villan)
P1
Battle 1: A Lone Prayer*
Battle 2: Let butterflies spread until the dawn
Battle 3: Normal Battle - Refine Version
Sub Boss: Deadline
Boss: Bloody Destiny
*Victory: School Days
P2
Battle 1: Normal Battle (Innocent Sin)*
Battle 2: Normal Battle (Eternal Punishment)
Battle 3: Quest Battle
Sub Boss: Boss Theme (Eternal Punishment)
Boss: Boss Battle (Innocent Sin)
P3
*Battle 1: Mass Destruction (P3 + P3F)
Battle 2: Wiping All Out
Battle 3: Wait and See
Sub Boss: Unavoidable Battle
Boss: Master of Shadow
P4
Battle 1: Time to Make History*
Battle 2: Reach Out To The Truth
Battle 3: Remember, We Got Your Back
Sub Boss: Reach Out To The Truth - First Battle
Boss: I'll Face Myself -Battle-
PQ2
Battle 1: Invitation to Freedom*
Battle 2: Pull The Trigger
Battle 3: Light the Fire Up in the Night "DARKHOUR" + "MIDNIGHT"
Sub Boss: Laser Beam
Boss: Nothing is Promised
(Music: Tack****: Vanilla, I only put it there for reference)
(****Music: Tack: Change from Vanilla)