Unable to merge two projects

I'm working on consolidating a number of similar unity projects into a single project for a third party. I was experimenting with exporting scenes and their dependencies from one subproject as a package and importing them into an empty superproject when I noticed that some scenes don't import at all. Once I've imported the scene from one subproject, the importer seems to think that a number of the scenes from other projects already exist in the superproject. This is constant even if I rename or move the scenes around in the superproject so that the scene imports won't overwrite them.

I suspect that the original projects may have been copy-paste-modified, and that this may have to do with UUIDs in objects. If this is the case, is there a way to regenerate the identifier that makes an object (scene) unique, so that I can import them instead of recreating them?