Gateway API defines a Kubernetes object that augments the behavior of an object in a standard way as a Metaresource. ReferenceGrant is an example of this general type of metaresource, but it is far from the only one.
Gateway API also defines a pattern called Policy Attachment, which augments the behavior of an object to add additional settings that can't be described within the spec of that object.
A "Policy Attachment" is a specific type of metaresource that can affect specific settings across either one object (this is "Direct Policy Attachment"), or objects in a hierarchy (this is "Inherited Policy Attachment").
This pattern is EXPERIMENTAL, and is described in GEP-713. Please see that document for technical details.