Maybe this tip might be helpful.
I ran into a situation when rigging that i wanted to make a brow and skull change to a mesh i had already sculpted shapes for. And the brow and skull changes would change the topology of the mesh (some edges/verts were removed others added etc.) So i decided to try out ZBrush to help solve this issue.
ZBrush has a projectAll function that is really incredible.
Here's a picture i made (original design, model) , that shows the new mesh (larger head in picture) projected onto the existing mesh (figure on right) (this one had some blendshapes already).
Then in Maya with a little help from Maya's wrap deformer I transfered (roughly) the brow shapes of the old mesh onto the new topology mesh. This is not an exact method as can be seen the brows still need some tweaking (bottom figure), but it does give us a starting point that is better than starting from scratch.
1-- we need the old topology mesh (one with blendshapes)
2-- new topology mesh (here one with larger head)
3-- *** And this is the special one , the new topology mesh BUT in shape of old topology mesh. This was where projectAll from ZBrush came in.
Now using a wrap deformer where, 3 is wrapped (neares face) by 1. (That is 1 drives 3 or in other case move a vertex of 1 means 3 gets moved)
So all our old blendshapes on 1 can cause 3 to move.
Now since we can get lots of shapes of 3's and the cool thing that --
we can go from 3, to 2. But How? Using a simple Blendshape.
So we can get all of our old shapes roughly onto our new topology mesh.
Hope this is helpful.