You cannot configure DHCP option 61 (client unique identifier) to prevent it from being sent from a client that is running Windows 8.1, Windows RT 8.1, or Windows Server 2012 R2.
To resolve this issue, install the November 2014 update rollup for Windows RT 8.1, Windows 8.1, or Windows Server 2012 R2.
After you apply this update, the following registry entry can be configured in order to change the behavior of the DHCP client so that it skips adding option 61 in a request:
By default, this registry entry is set to 0 (False),and therefore the option is included in outgoing DHCP requests.
Set this value to 1 (True) to prevent the option from being sent in the DHCP requests.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
See the terminology that Microsoft uses to describe software updates.