Configuration Manager Service Window Maintenance Mode Automation Override Mangement Pack includes a Wildcard Group which includes all systems. There is an override on this group to disable the "SCOM Agent Initiated Maintenance Mode Rule for Active SCCM Service Windows" rule for all systems contained in that group. If you want to test the functionality of the rule, open the group, click the "Excluded Members" tab, click the "Exclude objects" button, change the "Search For:" to "Windows Computers" and type in the system you are looking for in the "Filter by Part of name" field. Add the selected item and click "OK". If you want to enable the Automation functionality for all systems, just remove the override.