title: Add or edit label on existing node pool in GKE
body: <p>I created GKE cluster with node pool, but I forgot to label the nodes...
  In Google Cloud Platform UI I can't edit or add Kubernetes labels for the existing node pool...
  How can I do it without recreating whole node pool?</p>
  
  <p><a href="https://i.stack.imgur.com/lEA9b.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/lEA9b.jpg" alt="The label field is unchangeable"></a></p>