Anchor field cannot be set in Blueprint.

I’m trying to assign it to the InitializationField of a Geometry Collection in ConstructionScript or BegenPlay, but none of it works. I’ve heard that disabling and re-enabling the simulation should work, but that didn’t help.
Surely there’s no way it’s such a terrible specification that you have to assign everything manually with the eyedropper? There must be a way to assign it in Blueprints. Can someone tell me how to do that?