If I had uploaded 10 mp3s (which I did) and tied to sequences, then realized none of the songs were consistent volume wise I would run the app and adjust all the mp3s on my laptop. Then i'd delete those original mp3s on the pi and then upload them all again from the laptop and keep the names the same. no need to recreate playlists or anything. This is assuming you aren't running a show while doing this because i'd suggest a different approach if that was the case to minimize impact on the audience.