Common Data Service Connector is not leveraging CDS capabilities for alternate keys. Apart from GUID, Get Record action should accept alternate keys as well. It's a very convenient and clean way of pulling a record from CDS.
Alternate keys avoid the need to list records, loop through the result (singular) to get the GUID to then update the record. This lack of functionality, together with the inability to upsert using the CDS connector forced me to build a custom HTTP request to Dynamics web API