An mp3 file is made up of a metadata header prepended to the audio data blocks. While the id3 header can be edited to enrich the file description, the audio data is a result of a lossy compression and cannot be enhanced a posteriori.
So, to upgrade the audio quality of a mp3 file, you have to acquire a new – better – copy of it.
How do you cope then with the migration of the id3 intel (such as ratings information) contained in the original files? Tag&Rename for mac is yet to come (sigh) and this specific problem looked simple enough that I decided to code a tool to solve it.
Replica is a python script that enables you to copy id3 metadata between files (and more).
Go to the project homepage for more infos, or just start using it by typing
pip install replica.