Had this doc in my tool Box – continues to come in use from time to time:

 

Excluding Systems from Receiving the SCMC Client

Edit the following Reg Key on the SCCM Site Server:

 

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If the “Components” reg key doesn’t exist manually create the Key:

Double-click ExcludeServers key to open the Edit Multi-String Window

Specify the name of each computer you want to exclude. Press the Enter key after typing each computer name to ensure that each computername appears on separate line.

When a computer is added to the ExcludeServers list, it is flagged in the site database with an installed status which prevents the client from reinstalling. So if you later remove the computer from the list, this flag remains. In order to install the client software, you have to clean the install Flag.

 

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