Smart update management

This is a tricky one, and at the moment of writing, no tool can do it flawlessly in every case (and, honestly, it is unlikely one will ever). What happens when I change a type of three EC2 instances from m3.medium to c4.xlarge? Will my m3.medium instances shut down and be replaced one by one by new ones? Will they be instantly destroyed leading to a few minutes of downtime? Or will the tool, just ignore the updated instance type? Or will it not and then just override old nodes and I will end up with three new nodes and three old EC2 instances that I have to remove manually? Solutions to this problem differ from platform to platform, which makes it more complicated for the tool to be platform agnostic.