This registry editing trick has been around forever, but still works in ConfigMgr 2012! In fact, it’s the preferred way to keep the ConfigMgr client software from installing on specific computers in your organization.

A couple NOTEs: This only blocks ConfigMgr client software when using the site-wide automatic push method. You can still use any other method to install the client, ex. manually running CCMSetup.exe. Also, this does not exclude the computer from being “discovered”, just that the client software will not be installed once it is discovered liked non-excluded computers.

To do it…

On the ConfigMgr site server, run the Registry Editor.

Navigate to the SMS_DISCOVERY_DATA_MANAGER sub-key which is located within HKEY_LOCAL_MACHINE/Software/Microsoft/SMS/Components/SMS_DISCOVERY_DATA_MANAGER

Locate the ExcludeServers key and edit the Multi-String value.

Enter the NetBIOS name of each computer you want to exclude. Each computer name must be on its own separate line.

Hit OK and close out the Registry Editor.

http://myitforum.com/myitforumwp/2012/02/01/same-as-before-excluding-specific-computers-from-becoming-configmgr-2012-clients/