It is Easier to Upgrade a version of Symantec Endpoint Protection.
Symantec Antivirus v.10.x to Symantec Endpoint Protection v.11.x to Symantec Endpoint Protection v.12.1
Symantec Antivirus v.10.x to Symantec Endpoint Protection v.12.1
However, there is no Easy Solution to Downgrade versions or Symantec Antivirus / Symantec Endpoint Protection
Administrators should have a choice of versions to be installed on their machines.
The requirement of Testing of any new Security Software is an Important before it is put on the Production Environment.
However, sometimes it happens that the Software may not be working hand in hand with certain softwares after upgrade is performed.
In such critical situations, it is important for an Administrator to quickly restore the machine by downgrading the Software to an Older version without Uninstalling and Reinstalling (to save valuable time)
A Tool specifically created for this purpose may do the Job OR if implementing this in the Upcoming Releases may help as well.