Is there any way to keep partial vertex normal after blendshapes

Hi, I have exported a model with blendshape, but after morph, some strange shadow appears, is there any way to keep partial normals on the mesh, keep them not calculating after I set blendshape weight. please help=.=
(I heard that Maya can lock some part of normals when making blendshape animation, could 3dmax also do that?)