Hi,
If you need to update i do not see any need to uninstall the endpoints. You just need to go the deployment rules and change the agent version, all your endpoints on that rule will receive the instruction to update and will attempt to download/install the new version from the cloud.
If you want to uninstall the agent remotely with msiexec you need the uninstall password mandatory and must consider the XXX string is specific for each EPS.msi installer. You will need the .msi files you used to install the agents and use a different msiexec command for each installer. For example:
msiexec /x {XXX-1} /qn /norestart UNINST_PASSWORD="uninstall_password"
msiexec /x {XXX-2} /qn /norestart UNINST_PASSWORD="uninstall_password"
That will uninstall the agent without any message to the customer in silent mode. But if you have a cloud based endpoint management, i would use push operations to uninstall the agents.
I would recommend to do the upgrade/uninstall tasks from the infinity portal.
You can check the admin guide also:
https://sc1.checkpoint.com/documents/Infinity_Portal/WebAdminGuides/EN/Harmony-Endpoint-Admin-Guide/...
Regards