We are not yet ready to install the new 5800 Scan Engine on our systems and I would like to prevent the DAT containing the 5800 engine from being installed on my systems.
but I also wondered if just simply disabling my Client task to install the DAT that day would prevent the engine update.
I would then re-enable the DAT update task the next day once the new DAT has been checked into our ePO server. Would this work or would I still get the 5800 engine when installing the DAT released on January 21, 2016?
I don't think that will work. DAT updates are done Incrementally or attempt to install a full DAT. Once you start the update process, it will discover the missing incremental DAT installing the engine in the process. From ePO, a task change must be made to remove the engine update pull process. Additionally, if the local VSE console still has the McAfee HTTP or FTP update tasks, the update may fail over to use the Public McAfee update and update the engine regardless of your ePO task settings.
In the link you referenced is the strategy closest to what you proposed. Use Option 2.