To get massive back up, you just need to click the little wrench icon on the massive plugin where you added massive to the midi track (where you drag an drop effects and files to side chain)
Never did it myself but you should be ableto drag and drop it in lives file browser.
There’s a setting in the preferences which allows you to open more than 1 copy of ableton at a time. You should be able to open up the 2 projects in different instances, and then just copy the midi/fx across. You’ll probably have to copy everything individually though..