High Sierra killed QT7 functionality. Can it be restored?

Any ideas about how to restore QT7's Pro functionality?

Open the registration window and re-enter the name under which you purchased the "Pro" registration code and the registration code you previously received from the Apple store.

Okay, I see now that you can edit on QT 8, but not as easily as on 7.

But I would love to get back the easy functionality of QT7 Pro.

If all you need is the linear editing and transcoding functions, then MPEG Streamclip is still available as a free download. Like QT7/QT7 Pro, it is no longer being actively supported but remains functional (albeit in a somewhat depreciated state) under High Sierra. However, it does not support the composite or masking features provided by the QT7 "Pro" upgrade but does adhere to most of its other features and keyboard shortcuts although the built-in player seems to be showing its ages. If you still have the old Apple MPEG-2 Playback component installed on your system, then it can even play, edit (at the GOP level), and transcode MPEG-2/AC3 PS and TS which QT7 Pro could not properly handle. In any case, you can download and try it to see it it meets your needs since it's free and does not require any registration code.

macOS 10.13.2 includes a QT Player version 10.4 (in the Applications folder.) To what QT are you referring?

Apple no longer sells the Pro upgrade to QuickTime Player 7.