Create a custom library from existing content?

I was wondering if there’s a way to, say, take some movies from my movies section and some shows from my shows section and combine them together to form another library that I can share. I’d prefer to do this in a way that doesn’t involve creating messy symlinks to a folder on the hard drive.

No, there is no way apart from the Symlinks.
On top of that it is not possible to combine tv shows and movies into one library, unless the shows lose everything what makes them shows (tracking which episode was watched, what is the nex episode to watch etc.)