I love mp3tag because it is very powerful for tag manipulation in batch processing.
The possibility to search / replace and use regular expression in the tags is awesome.
I however found a missing action that I believe would be nice: Add
From the menu "Actions > Actions" (ALT +6), then I edit one of the existing Action groups or create a new one. I don't see an option to add a string.
An example for this option: add a string in the genre field such as "Top40"
Also, adding a Trim option to remove the first or last X characters or digits would be nice.
As an example, itunes m4a fles have the Year filed in this format: 2012-03-30T07:00:00Z.
I usually trim the first 10 characters.
Thanks for this awesome tool !