After you have created a blend shape deformer for the base object using multiple target objects, you can swap the order of the target objects. This changes the order in which the target shapes are applied to the base object, which affects the sequence for shape animation.
To swap two target objects
In the Shape Editor, you can easily change the order of target shapes by dragging them up or down within their Blend Shape Deformer list. This has the same effect as using the Swap command.