Hello,
It is important to let you know that without restart, removal of Symantec Endpoint is difficultdue to the Firewall Driver. Driver could not be removed without a restart.
In other words, even if you uninstall SEP by surpressing the restart, it would not be completely uninstalled.
However, Take a glance at these 2 links and let me know if this answers your question.
http://www.symantec.com/connect/forums/uninstalling-sep-remotely
http://www.symantec.com/connect/forums/remote-uninstallation
https://www-secure.symantec.com/connect/forums/uninstall-client-remotely
Question comes in my mind, why uninstall when you want to install it back??
Incase, you want to Migrate to the Latest version, then you can simply Migrate the SEPM (check the Article below)
Upgrade and migration resources for Symantec Endpoint Protection 12.1
Once, the Migration of SEPM is performed, you could simple create a custom package (without restart option) check this thread -
Creating custom client installation packages in the Symantec Endpoint Protection Manager console version 12.1
Hope that helps!!