Update a shapekey Basis from another shapekey I am editing a character that has many shapekeys for facial expressions. I have made some changes to the character's overall face to adjust its features (no vertices added or removed though.) I have done these changes as their own shapekey for convenience.

I now want to add these changes into the Basis without breaking all my other expressions. I have found that I can move my changes to be second in the list after Basis and delete Basis, and my changes are now the new Basis. However, it does not work with my expression keys, as when I use them, it undoes the changes I made by moving vertices back to their position in the original Basis, even though these points are not usually moved by the expression keys.

My expressions currently work properly with my changes as their own shape key. How can I make the changes into my new Basis and also update my expressions to behave the same way?
Let's say you have 3 shapekeys: Base, new Face, expression.
The first is the old mesh, the second the new modified mesh, the third the old expression movement you want to preserve.
Select the object and the basis mesh, enter edit mode, select all vertices, Ctrl V "Blend from shape": in the toolshelf (T) in the bottom left of the 3D view you will have to choose the "new Face" shape key, and set an amount (Typically 1.0).
Exit edit mode and you should have your expression shape key working on the new face.

Once you understand the principle you will have to tweak the values and the shape keys, maybe propagating not all but only some vertices, setting the amount not to fully 1.0, or tweaking your old expression shape keys, but you will have a good starting point.