Would be really nice if the blendShapes are dependent by the basic geometry - remodel only the basic one - update the blends automaticly.
I will use a simple scene with 3 spheres to keep the things simple ...
The left two spheres are blendTargets, the right one is the baseShape ( deformed object ).
In fact this simple technique works with all the deformer types. We can easily change the topology of any skinClustered geometry without messing-up too mutch the construction history. To do it fallow the next steps:
1. Add a empty transform node - "createNode transform";
2. Display the intermediateShape ( with command "DisplayIntermediataObject" from the "Deform" menu ) of the skined shape, and parent it under the empty transform node - "parent -add -s theNameOfTheIntermediateShape theNameOfTheNewTransform". This will create isntance of the intermediate shape.
3. Apply whatever you want modifications over the instanced intermediate shape and then delete its construction history.