defaults.yml

#@data/values
---
topologySpreadConstraints:
  - maxSkew: 1
    topologyKey: ""
    whenUnsatisfiable: "ScheduleAnyway"

demo.yml

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

#@ def labels():
app: echo
org: test
#@ end

kind: Pod
apiVersion: v1
metadata:
  name: echo-app
  labels: #@ labels()
spec:
  topologySpreadConstraints: #@ data.values.topologySpreadConstraints
  containers:
  - name: blub
    image: hashicorp/http-echo