Regarding MP3Tag v2.40a (beta).
Shorten the width of all the fields enough so they do NOT exceed the width of your screen, and there is some unused space on the far right hand side.
If you right-click on an existing field, you get a 'customize columns..' pulldown as expected. However...
If you right-click on the far right hand hand side, past the last of your fields, MP3Tag crashes.