Hipocrazy, this has been discussed already, though can't recall if a WM tag editor ever surfaced. I use PocketMusic and it has a tag editor, but I doubt the free version supports this and even the full $20 version has only a text editor. That other thread may have something for you. Its subject header was "MusicID and Tagging" in the Vogue forum. Here's a link:
http://forum.ppcgeeks.com/showthread.php?t=32876