Add tags for .m4a-files (iTunes) in Mp3tag?

Is it possible to add tags to .m4a-files (iTunes) in Mp3tag?

I've downloaded some songs from what.cd that originally is downloaded from iTunes, so therefor I can see how bought it etc etc... If I insteed wanna write my name there, how do I do then? Cant see that tag in mp3tag. I can find "%itunesaccount%" but nothing else.

I also wanna detele the that encoded by tag. Not the same as ENCODEDBY in mp3tag.

You can see the tags in iTunes by -> click a song -> show info.

Hope someone understand what I mean?