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.)
Paste text contents of the clipboard to each of the selected tracks' Lyrics tag
Batch set new Last Played/Last Skipped of selected tracks
Enter text for the selected tracks' Description tag
Remove iTunes tracks disassociated from files
Delete characters from the beginning or ending of selected tracks' name, artist, album, comments, composer, or show tags
Exports and then re-imports selected tracks' artwork