After you create a blend shape from a mix of target shape weight settings, you can bake the base object's current blend shape state into a new target shape.
Choose
Create > Add Selection as Target in the
Shape Editor. Select
if you want to create different types of target shapes (tangent or transform types).
Maya creates a new target shape for the blend shape deformer, and it appears in the
Shape Editor.
Drag the new target shape's weight slider to reach this new target shape as the blend shape on the base object.