config.yml

---
kind: ConfigMap
metadata:
  name: habor-core-ver-43
spec:
  original_stuff: 1

overlay.yml

#@ load("@ytt:overlay", "overlay")

#@ def name_startswith(name):
#@   return lambda idx, left, right: left["metadata"]["name"].startswith(name)
#@ end

#@ is_config_map = overlay.subset({"kind": "ConfigMap"})
#@ habor_configmap = overlay.and_op(is_config_map, name_startswith("habor"))

#@overlay/match by=habor_configmap,expects="1+"
---
spec:
  #@overlay/match missing_ok=True
  additional_stuff: null