Hello,
Thanks for the discription.
Here, before you add the Install Packages, you would have to create seperate custom packages which would not ask you machines to restart.
To do so, check the articles provided below:
1) How do I create and configure a custom Symantec Endpoint Protection installation package in version 12.1?
https://www-secure.symantec.com/connect/articles/how-do-i-create-and-configure-custom-symantec-endpoint-protection-installation-package-vers
2) Restarting client computers : http://www.symantec.com/docs/HOWTO55111
Once, these settings are in place.
You can then add install packages to the each clients. Then the clients taking new install packages. After the client complete download install package , It is Asking Restart the client system .
These steps would help you...!!!