The key is you don’t want to change the file, because that’s where the field is. When you change the file, you’re changing the field and you risk damaging the field.
In your plans of your question, you’ll be changing the file in two places: changing the volume that the original file was recorded at and changing the file format (from .mp3 to .WAV). This last bit is why downloading or converting a YouTube field renders it ineffective.
As I said above, you don’t want to be changing the file or the data in it. (This is why most of use “playlists” rather than turning out playlists into a single track. Plus playlists make it easier for us to evolve our playlists as we accomplish individual goals.)
I’m told there are some music players which adjust the volume of the individual tracks of an album or playlist. Since it’s the player that’s performing this “normalization,” it’s doing this in the normal course of its translating of the file data. So, the field is unaffected.