I add a common Collection tag (item Edit > Tags > Collections) to entries I want to group together, you can also assign multiple Collection tags to assign them to various groups. It’s tedious to setup because you can only tag them individually, but once they are they’ll show as a collection named by the tag.
If you want to exclude them from your general library, the only way I can think of is to move them into a directory not under it and create a separate Plex library entry pointing at it.
Don’t eat shit, mulch the rich.