Replacing Mesh - Object in animation

For the animation I’m working in, i need to turn an old lady to a young one.
Some kind of “metamorphosis” —
I know I could use some morph keys , but for that I will need to keep the same shape and just play around with vertexes.
So I’m wondering if, beside the visibility key, or compositing, there is a way to replace a mesh with another AND animate that parameter (that’s the problem)… That would be great for southpark like lip syncing, I think

Check out shapekeys.