OS X 10.8 or later. This applet will assist with swapping, copying, and appending data between two user-chosen tags in selected tracks or tracks in the selected playlist:
Swap - swap data between tags, ex: ARTIST<->COMPOSER
Copy - copy data from one to another tag, ex: ARTIST->
Append - append data from one tag to the end of another, ex: ARTIST->COMPOSER - ARTIST
Prepend - prepend data from one tag to the beginning of another, ex: ARTIST->ARTIST - COMPOSER
The latter three actions also provide an option to delete the info from the first tag after the copy. Read Me explains all.
This update is free for registered users of v4.x.
Select the Action to perform between the two chosen tags in each selected track.
Two scripts copy text from clipboard to current or single selected track's lyrics tag
Remove iTunes tracks disassociated from files
Selected track plays after current track ends
Convert selected tracks and export the converted files to a new folder
Displays files in iTunes Media folder not in iTunes track library
Locates pairs of track entries pointing to the same file