Make my own Megascans assets a Starter Content folder ?

How might I make all the megascans assets I have ALREADY downloaded to a project, a default starter content folder, so I can add all those assets to any project I create ?
Can all my assets not be used from ONE location for all projects ?

I’d like to do the same with a lot of my assets as opposed to always duplicating the entire project just to test out other things with it.

How do I set up a custom shared folder for all projects ?

Why would you not want the assets to live uniquely in each project though? It seems like the easiest thing would be to create your modified starter project, then clone it whenever you want to try out variations (be sure to leave the original untouched). Also for megascans in my experience the easiest technique is to just drag the folders from the Bridge library to the content browser in UE4, that would be faster than duping the project and maybe get around your issue.