A LiveUpdate session runs automatically after an install of Symantec Endpoint Protection (SEP).  Is there any way to prevent this? 

There are multiple ways to prevent LiveUpdate from running.

MSI script:

Add the "RUNLIVEUPDATE=0" to the MSI command

Refer to TECH102668 for the details of using MSI command line switches and scripting of SEP installation

Exported Install Package

When a install package is exported without the "create a single .EXE file for this package" option selected you can edit the setaid.ini or the setup.ini files within the same directory as the setup.exe file for the install package

setaid.ini*

Change the "CONNECT_LU_SERVER=1" entry to "CONNECT_LU_SERVER=0"

setup.ini

This file contains the MSI string used to install SEP. Add "RUNLIVEUPDATE=0" to the string

*settings in the setaid.ini file will override any settings in the MSI command string