Similarly I would like to update an existing urlmap, mimicking the
gcloud compute url-maps add-path-matcher
command and add host-rules and path-matchers to an existing urlmap. this would give me the ability to decouple the creation of the loadbalancer, frontend, firewall rules, targetproxy, initial urlmap, etc.. that our infra team creates and the host-rules and path-matchers with their associated backends that the dev teams would be responsible for.
it looks like the regionbackendservice and backends are coupled together, similar to the regionalurlmaps and host and path-matcher objects. i was hoping i could add gke service backends without updating a centralized program that has the urlmap with all mappings defined but that doesn't seem possible.