This script will apply user-entered text to the "Description" tag of each of the selected tracks. iTunes 5.0.1 or better.
(Note: In order to launch this PowerPC-era script on an Intel machine, it must first be opened and then saved using AppleScript Editor, which is located in your /Applications/Utilities/ folder. More information is here.)
Perform search-and-replace on text in your choice of tags
Set choice of various number tags of selected tracks incrementally
Delete characters from the beginning or ending of selected tracks' name, artist, album, comments, composer, or show tags
Batch merge and/or delete playlists
Renumber order of selected tracks
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