>>349384924
Not all of the models change the mesh to do a facial expressions
What some people do is have a hidden mesh inside the head and to make certain expressions they make that mesh to appear on front of the face.
Just to give an example, my avatar has tears hidden on the head, the blendshape just moves the tears and makes them bigger. Another example would be when making a blushing face, the blush is also hidden inside the head and by using a blendshape it makes it bigger and it appears on the face of the model.
You can use UV offsets, but you have to set that up on unity.