gcloud alpha compute machine-images set-iam-policy

gcloud alpha compute machine-images set-iam-policy - set the IAM policy for a Google Compute Engine machine image
gcloud alpha compute machine-images set-iam-policy MACHINE_IMAGE POLICY_FILE [GCLOUD_WIDE_FLAG]
(ALPHA) Sets the IAM policy for the given machine image as defined in a JSON or YAML file.
Machine image resource - The machine image to set the IAM policy for. This represents a Cloud resource. (NOTE) Some attributes are not given arguments in this group but can be set in other ways. To set the [project] attribute: provide the argument [machine_image] on the command line with a fully specified name; set the property [core/project]; provide the argument [--project] on the command line. This must be specified.
ID of the machine image or fully qualified identifier for the machine image.
Path to a local JSON or YAML formatted file containing a valid policy.

The output of the get-iam-policy command is a valid file, as is any JSON or YAML file conforming to the structure of a Policy.

These flags are available to all commands: --account, --billing-project, --configuration, --flags-file, --flatten, --format, --help, --impersonate-service-account, --log-http, --project, --quiet, --trace-token, --user-output-enabled, --verbosity.

Run $ gcloud help for details.

This command uses the compute/alpha API. The full documentation for this API can be found at: https://developers.google.com/compute/docs/reference/latest/
The following command reads an IAM policy defined in a policy.json file
  and sets the policy for the machine image `my-image`:
gcloud alpha compute machine-images set-iam-policy my-image policy.json

See https://cloud.google.com/iam/docs/managing-policies for details of the policy file format and contents.

This command is currently in ALPHA and may change without notice. If this command fails with API permission errors despite specifying the right project, you may be trying to access an API with an invitation-only early access whitelist. This variant is also available:
gcloud beta compute machine-images set-iam-policy