A several step process.
Create a agent policy which uses the previous branch for the engine, create an "Engine Update" tag.
Create a query for 5600 engines, apply "Engine Update" tag to systems you wish to update
Run a Tag query as a server task and have it apply the previous engine policy, then wake up the Agents.
Some time later, using the same Tag query, run another server task to send an "Update Now" task to the systems.
Again some time later, run the Tag query again to roll the Agent policy back to where is was and wake up the systems.
Query for systems with the new engine version and the tag, then remove the "Engine Update" tag.
Thanks for your reply. I will follow the steps provided and update you with the status.