If you wish to stop new scheduling manager instances (AutoSys, dSeries, ESP, etc.) from registering with a System Agent the procedure is as follows.
Release: All Supported Versions
Component: CA System Agent
https://techdocs.broadcom.com/us/en/ca-enterprise-software/intelligent-automation/workload-automation-system-agent/12-0/troubleshooting/troubleshoot-ca-wa-system-agent-for-unix-linux-windows-iseries-or-hpe-integrity-nonstop.html