Before I start, I will say that you can only have up to 3 custom songs. Also, this, to my knowledge, has no possible way of breaking your game if you do everything I say.
Before starting, make sure the game itself is not open. Step 1- Open the Launcher, then Settings Step 2 (For windows users)- Copy the Installation Directory, click Windows+R, and paste it in there and click enter. Step 2 (For non windows users)- Do whatever you normally do to open folders, but go to the folder shown. Step 3- Go to Audio, then BGM Step 4- Get a music file of your choice, preferably a .mid Step 5- Find the files named Radio - Name.mid in the BGM folder Step 6- Rename them Radio - Name(Original).mid Step 7- Take the music file of your choice and name it Radio - Name.mid Step 8- Put the file in the BGM folder Step 9- Open the game Step 10- Go to radio and test the music.
Also, since there are 3 different radio songs, you can change all 3, but just remember which song is actually what. I made Oak’s song turn into Audrey’s song. If you ever want to have the original song back, just delete the custom one, then edit the one named Radio - Name(Original).mid and get rid of the (Original) and that should work.