The new Get Info panel setting, "Show composer in all views" does not have AppleScript support, unfortunately. I suppose we can hope it might be added in the future. It can still be batch-set by selecting tracks and editing information for multiple items.
Apple has released an update to iTunes that accommodates the just-announced iPhone SE and 9.7-inch iPad Pro. It's available from the Mac App Store under the Updates tab. Kirk has a rundown of new (somewhat minor) features.
Apple has updated iTunes to 12.3.2 with improvements to browsing works, performers and composers for Classical tracks in Apple Music. More as it develops.
Just noticed the most recent iTunes sdef (12.3.1) now contains a genius flag for user playlist. Sometime around iTunes 12, Apple made Smart and Genius playlists both respond to smart and you couldn't tell the difference. It is now possible to distinguish Smart and Genius playlists with AppleScript. Thanks!
Title about says it all. No specific changes mentioned except for "overall stability and performance" improvements.
Apple released iTunes 12.3 today. It adds support for iOS 9 and OS X 10.11 (El Capitan) and two-factor authentication. It also fixes some issues with Up Next sorting, radio stations not appearing in Recently Added, and problem coordinating loved songs.