We've had several customers already asking how to customize the hostnames of the overcloud nodes using Openstack Director Operator, but it seems it would only use what it's specified on the HostnameFormatDefault of each role. So it won't work.
Customers keep relying on HostnameMap but that is only creating the Ansible inventory now.
I think a note saying you can't customize hostnames would be useful to avoid more cases like this.

https://docs.redhat.com/en/documentation/red_hat_openstack_platform/17.1/html/deploying_an_overcloud_in_a_red_hat_openshift_container_platform_cluster_with_director_operator/index