Adding More Total Songs

Would I change those 2 songs to the ones I want, and then re-add Returner and Factory in my expanded msucis and change the map data that uses those to point there? I'm probably making this more complex then it needs to be.

These are song IDs that formations can use. I think you could use the last entry because I believe it is a dummy entry. You will have to check that no formation except the one you want use this entry.

If you add a new song, write 55 instead of FF and check the checkbox in FF3usME for the formation(s) to use your song.