How do I copy mp3s and then edit the ID3 tags of the copies without altering the tags on the originals?
As to your second question, I would try Tagscanner (https://www.xdlab.ru/en/). You can tell it the location of the files you want to edit tags for. So there is no danger of editing the set wrong files. It also has a batch mode. Read the documentation, as with many powerful tools, it has a lot of features that can seem overwhelming to new users. It also has a preview mode for changes that allows to to see the changes you are making before committing them.