So, as a follow up, what about a more complex situation:

Clustered default instance of SQL Server with different virtual IP address and network name then the virtual name and address of the clustered Windows server it is installed on. (note: virtual as in cluster naming, not as in virtual server stuff).

The @@ServerName reports the SQL cluster name, while serverproperty('servername') reports the Windows cluster name. I do not want to change @@Servername to match serverproperty, I want to make serverproperty match @@Servername. How is this done in a clustered situation like this?