I don't think a rule is required.

If the existing service configuration explicitly states that the port over which the service can be contacted, then that's OK, as that configuration will still be valid.

Migration Guide description
Services that are exposing http ports are now automatically mapped to port 80. The change makes the generated Service easier to consume by external tools, or services as knowledge of the actual container port is no longer needed by consumers. This may affect services that were using the service dns name and container port combination to communicate with each other.

Migration Guide link