OS X 10.8 or later. Append the same user-entered text to the beginning or ending of the existing text in the chosen tag (Song Name, Artist, Album Artist, Album, Composer, Comments, Genre, Grouping or Show Name, and their Sort siblings) in each selected track.
For tags other than "Song Name" and "Show Name", this script may be just slightly less involved than performing a multi-edit on the selected tracks.
Also see This Tag, That Tag.
Preview each track as it will appear after applying the entered text.
Export selected playlists as individual XML or M3U files
Copy chosen tag info from one set of tracks to a different set of tracks
Convert selected tracks and export the converted files to a new folder
Display, create text file listing info of dead tracks
Batch-append text to comments
Remove iTunes tracks disassociated from files