I tried following the instructions given, but I haven't been able to get this working. So please allow me to post the steps I've done, so you can correct me on what I didn't do correctly or at all.
First, I downloaded the psf files, which were saved in the following directory.
I then loaded up the .dll files as shown here.
I also have a folder of the custom music that I WANT to use....
And then pointed to that path here.
So in this test, I'm trying to replace the opening Bombing Mission BGM with the song I want to use. I tried renaming it the same way as the psf file (as instructed), but it doesn't replace the midi music.
I'm certain I'm doing something wrong, but I would appreciate if you could tell me what that was.