You may have to do it in the WSUS panel and not patch manager. Im not 100% sure as ive never done in in SPM but under options > sources and proxy> there is a checkbox for "this is a replica server" Just uncheck that.
As for your second question I have no idea what you mean. A list of computers to go under WSUS? You assign via GPO to use WSUS with either the console or GP assign the target group for WSUS. Either way you set up a GPO to tell the PCs to use WSUS.
Ignore the second point, i found my way around it.