I'm not really sure about this but as far as VSE 8.8 does not have a "real" DAT included in the package (it has a kind of fake DAT with version 1111) you won't be able to decide wether to update or not at the end of the install process even if you use your specific command, it will always update.
Perhaps you may be interested on using McAfeeInstall Designer where you'll be able to create a new package with a DAT inside and (Ithink) you'll be able to decide if an update will take in place after install or not.
The installation requires an autoupdate at the end of the install as the install only lays down placeholder DAT files (1111). If you do not want the update to occur at the end of the install, then you will need to make a MIDpackage that includes DAT files current enough (no more than 35 days old) to not kick off an update.
The installer checks to see if the DATs are current at the end of the install, if not...then an update is performed. The only way around this is to have current DATs on the box, which means for new installs using MID.
Behaviour was changed between versions thats correct.