macOS 26
UPDATED: This Tag That Tag v6.4
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->COMPOSER ARTIST
Append - append data from one tag to the end of another, ex: ARTIST->COMPOSER - ARTIST
Prepend - append 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 app is free to try full-featured in Demo Mode. In Demo Mode it will only process 12 tracks per launch. If you like it you can purchase a code for $1.99 which will unlock the 12-track restriction. Launch the app and click "Register..." in its File menu to make an in-app purchase.

Latest version:
- Accommodations for macOS 26/Tahoe
More information for This Tag That Tag v6.4 and download link is here.
Bug or Feature? Non-Persistent Permission to Read the Media Library
If you've been following along, you will have noticed how Apple has, over the years, gotten stingier with which and how certain "protected resources" on your Mac can be accessed by third parties. One of these resources is your Media library. In order to access information about your Media library, a third party app has to declare its intentions to the user. This is a typical dialog you will see in such a situation:

Conventionally, this will be displayed as you launch the script app for the first time. Then the user's "Allow" decision will be remembered every time you launch it thereafter.
This is not happening in macOS 26/Tahoe. Every time you launch such a script you will see this dialog.
Not every script requires access to the Media library so this doesn't happen with every script. But it does with enough of the popular ones.
I'm not sure if this is the intended behavior. I filed a bug report.
UPDATED: Search-Replace Tag Text v7.4
Performs a search-and-replace on the text in your choice of track tags in the Music or TV app (Title, Artist/Director, Album Artist, Album, Composer, Comments, Genre, Grouping, Show, Movement or Work) in the selected tracks or all the tracks in the selected Playlist. Features case sensitivity and whole word match options and "Test run" preview.
This app is free to try in Demo Mode. In Demo Mode only up to 5 tracks can be processed per launch. You can purchase a code for $1.99 which will remove the 5-track Demo Mode restriction. Launch the app and click "Register..." in the its File menu to make an in-app purchase.

Latest version:
- Accommodations for macOS 26/Tahoe
More information for Search-Replace Tag Text v7.4 and download link is here.
