Downgrading iTunes 12.7 to 12.6 on High Sierra:
I had a big complaint with the new version of iTunes. Specifically, Apple decided to remove the ability to access ringtones on the new version of iTunes (12.7), which also meant that the functionality of creating ringtones in Garage Band was rendered useless because there was no way to export (share) a ringtone into iTunes and there's no option of being able to save it anywhere else.
I thought it was a glitch and upgraded my OS to High Sierra, hoping to resolve the issue, but it was an intentional move by Apple to remove the feature.
The solution I found was deleting the newest version of iTunes using the Terminal app in the Utilities folder of my Mac and reinstalling version 12.6.3. The article in this link details the simple steps needed to do it:
http://osxdaily.com/2017/09/17/downgrade-itunes-12-7-to-itunes-12-6/
Just so you know, the article stresses the need to backup your computer before performing the update (which is VERY good advice), but I went right to it without backing up and had no issues.
Apple's decision to cripple the functionality of iTunes and Garage Band while claiming it "focuses" iTunes on music, movies and podcasts is clearly a ploy to funnel revenue into the Apple Store and train its newest customers to expect less and pay more.
Shame...