Please see this FAQ – https://docs.microsoft.com/en-us/azure/api-management/api-management-faq#is-the-api-management-gateway-ip-address-constant-can-i-use-it-in-firewall-rules. If you don’t re-create API Management instance on every deployment the IP address will remain the same (and deployments will take significantly less time too). Does this address your concern?
Work has started on both moving capabilities that are only available in the CDN Supplemental Portal (e.g. rules engine) into the Azure Portal and also providing API’s to support all of these features. This work will be done in multiple phases over the next several months.Masi Malmi commented
Yes, really looking forward to this capability. Cannot believe this still requires manual steps, it would be very important to be able to automate the rules engine part for instance to ip restrict CDN content of test environments.