You can replace a shape key (source) with a new shape. When you do this, any existing clips that use the source are also updated, and new clips from this source will be based upon its new shape. Only the shape key you're replacing is affected: all other shape keys remain the same.
For example, let's say your client wants to change a few words so a different shape is required for a phoneme. You change the original model and then replace the old shape key with the new deformation.
Select Shape Modeling from the Construction Mode list on the main menu at the top of the interface.
At the appropriate frame, deform and transform the shape-animated object or cluster into a new shape.
In the explorer, expand the Mixer 
Sources Shape folder and select the shape key you want to replace with the new one.
Choose Deform Shape Replace Shape Key from the Animate toolbar, which replaces the shape key at the current frame with the new shape you have selected.
The modified object is stored for the selected shape and the new shape is used in the animation.
Duplicating Shape Keys (Sources)
When you duplicate a shape key, you can rename the duplicated shape keys with more descriptive names as soon as you create them so that you can identify them later in the mixer. You can rename a shape key as anything else in the explorer (for example, click the shape key name, press F2, and enter a new name).
All shape clips in the mixer referencing that source are updated with the new name.
