There are several use cases where there is need to associate existing Enterprise setup with new or changing domain where deployed machines FQDN are changing from xxxxxx.domain-one.com to xxxxxx.domain-two.com etc.
As ArcGIS Server already supports machine name renaming from the ArcGIS Server administrator GUI, also ArcGIS Data Store (relational) is able to adapt to the new machine name, BUT Portal doesn't support this kind of operation.
Add Portal renaming capability to the Portal Admin GUI.