Many people don't know how to add music for game over screen. Well, I realized and I tell you now, so here you go:
1. Copy the music (yourmusic.mp3) you want for your game over screen to "data" folder
2. Open gameover.def and add the following code:
bgm = yourmusic.mp3
bgm.loop = 1
3. Save the gameover.def file and you're done!