Hello,
Since you are using SEP SBE 12.1, the auto-upgrade uses the default packages to upgrade. You can disable this feature in case you want to -
How to disable the auto-upgrade feature for clients in Symantec Endpoint Protection Small Business Edition 12
http://www.symantec.com/docs/TECH96955
In your case, You can create a custom package and then you use any of the deployment methods.
Creating a Custom Package in Symantec Endpoint Protection (SEP) Small Business Edition (SBE) 12.1
http://www.symantec.com/docs/TECH190756
About client deployment methods
http://www.symantec.com/docs/HOWTO81302
Preparing Windows operating systems for remote deployment
http://www.symantec.com/docs/HOWTO81300
Hope that helps!!