How to patch existing resource?

[arul-gupta]

Is there a way to patch an existing resource like kubectl patch?
Use case being patching the cni plugin that is already installed on an EKS cluster. Kustomize can only patch manifests that are part of the repo.
I thought of using custom plugin but repo-server cannot access the api-server to fetch the current resource manifest.

[gabegorelick]

See #2437 for potentially relevant discussion.