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.
Rename selected tracks' Song Names with their filenames (minus extension)
Use tag data to formulate new file name for selected tracks' files
Exports and then re-imports selected tracks' artwork
Remove iTunes tracks disassociated from files
Append user-entered text to beginning or ending of selected tag of each selected track
Set the Plays of selected tracks.