You
can't grant yourself admin access with the official build. Only the Graphene devs have the ability to push changes to the OS on your phone. Yes you can fork the software and build a version with your own signing key, then wipe your phone and install your custom build and thereby take back control, but then is that really still Graphene?
I think it's fair to say that that's at least borderline anti software freedom, even if it's true they have good security reasons for doing things that way.