According to the official documentation (https://docs.openshift.com/container-platform/4.17/registry/configuring_registry_storage/configuring-registry-storage-aws-user-infrastructure.html#registry-operator-configuration-resource-overview-aws-s3_configuring-registry-storage-aws-user-infrastructure) there is no way to configure custom tags for s3 buckets created by the image-registry-operator.
And it also ignores tags which were configured in the initial deployment config.

    Deploy OCP on AWS with some custom tags in the installer config. They won't be visible on the s3 buckets which are created by the registry operator.

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    Created s3 buckets should have at least the same tags as the rest of the created infrastructure.