Manually patch some of the instances, and then perform a rolling restart on the instance group.

Using the new instance template, perform a rolling update across all instances in the instance group. Verify the new feature once the rollout completes.

Deploy a new instance group and canary the updated template in that group. Verify the new feature in the new canary instance group, and then update the original instance group.

Perform a canary update by starting a rolling update and specifying a target size for your instances to receive the new template. Verify the new feature on the canary instances, and then roll forward to the rest of the instances.