How To Downgrade iTunes 12.7 on Mac
1. Back up the Mac if you haven't done so already
2. Close your iTunes if it's running
3. Open the Terminal application in Mac OS and type the following command lines, then hit return:
4. Now you'll be in the Applications folder via command line, the next command syntax must be precisely entered to remove iTunes, make sure the syntax is exact:
sudo rm -rf iTunes.app/
5. Be 100% and absolutely certain that your syntax reads the same, rm is unforgiving and will delete any file permanently it is pointed at. When confirmed you are pointing at iTunes.app/ only, hit return and authenticate with an admin password to completely delete iTunes.
6. After it finished, go to the Finder of Mac OS and visit your user ~/Music/iTunes/ folder and locate the file named "iTunes Library.itl" and move it to the Desktop.
7. Still in ~/Music/iTunes/, Open "Previous iTunes Libraries" folder and find the most recent dated iTunes Library file and make a copy of that file
8. Drag the copy of "iTunes Library 2017-09-12.itl" to the ~/Music/iTunes/ folder and rename it to "iTunes Library.itl".
9. Download iTunes 12.6 here > Install it on your Mac, then launch iTunes once complete. That's it, you're now successfully downgrade your iTunes from 12.7 to 12.6.