Hey, I couldn't find anything about this, so sorry if it's already been addressed, but is it possible to change the battle music in FFTA?
Well, probably. Darthatron changed the main theme a couple of times to the best of my knowledge, like here (https://www.youtube.com/watch?v=kBPDokz36zY).
I believe he details how he did so somewhere, I can't at all recall where though, maybe some video.
Good to know that it's probably possible, at least! :D
Just gotta figure out how now lol
EDIT: Does Darthatron still post here ever?
Not sure if you were still looking for information on hacking the battle music for FFTA, but just in case...
Modifying music in GBA ROMs is actually pretty straight forward, but like all rom hacking it's pretty tedious, since your music won't always turn out how you want. But with some patience, midi editing skills, and ... I don't know. Spoonfuls of peanut butter. You can make the music mod of your dreams with FFTA~ /o/ (or with any GBA ROM)
The best guides I've found, that I can think of off the top of my head, are from these sources:
http://www.feshrine.net/hacking/Fire%20Emblem%20Music%20Hacking%20Tutorial.pdf
https://www.pokecommunity.com/showthread.php?t=121856
http://pokemonhackersonline.com/showthread.php?t=120
And an example of what's been done in the past:
https://www.youtube.com/watch?v=JDOORFyVT6w
Google is definitely your friend, here. Other communities have made some stellar progress with music hacking. The easiest and most quick and dirty way of changing a song is obtaining a MIDI, converting it to a .s file using mid2agb, and then assembling the song into the rom using a tool called Sappy. It probably won't be a very clean and satisfactory way to do it but it can be that simple sometimes. You'll need to edit instruments and tracks, loop the music, maybe even try porting Blazer's All-Instrument Patch to FFTA to make things just sound nicer from the get-go, but for now I recommend finding all the GBA Music Hacking guides and tools that you can. There are bunches~ ^^