$ kubectl label po green-5c8f858bbb-mqxrd app=blue pod-template-hash=5bc56d75b --overwrite
NAME READY STATUS RESTARTS AGE LABELS
blue-5bc56d75b-5j462 1/1 Running 0 15m app=blue,pod-template-hash=5bc56d75b
blue-5bc56d75b-wwn8c 1/1 Terminating 0 27s app=blue,pod-template-hash=5bc56d75b
green-5c8f858bbb-bsjwv 0/1 ContainerCreating 0 0s app=green,pod-template-hash=5c8f858bbb
green-5c8f858bbb-mqxrd 1/1 Running 0 15m app=blue,pod-template-hash=5bc56d75b
green-5c8f858bbb-s564q 1/1 Running 0 15m app=green,pod-template-hash=5c8f858bbb
green-5c8f858bbb-x7hmh 1/1 Running 0 15m app=green,pod-template-hash=5c8f858bbb