As of version 4, iTunes has a "Replace Existing" option when users are re-importing CD tracks to replace existing tracks. The problem is that iTunes will only allow this option if the ID3 info for the CD tracks and the current iTunes tracks is identical. This script writes the writable info from selected tracks to the info of a CD; when you re-rip, the CD track data is already the way you want it.
(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.)
Copy number prefix in Song Name of selected tracks to their track number tag
Perform search-and-replace on text in your choice of tags
Capitalize the first letter of each word in selected track names
Add or subtract a user-entered number from each selected track's Plays
Create a text file containing an alphabetical list of chosen tag data
Export artwork of selected tracks to parent or specified folder