How to align two curved surfaces of the same object? I have a mesh that is folded around an edge and curved. Currently, both curved parts are already aligned very closely, but not perfectly. I would like to align them more precisely with some fixed distance in-between.
Important conditions:

the operation must be non-destructive; the surface must retain its vertices in unchanged order because it has shape keys attached
I don't care which parts of the surface will be aligned - it could be the lower part aligned to the upper or vice versa or even both aligned to some average positions in-between


How do I do that in Blender 2.92 ?
Edited:
All the modifier based solutions seem to be inappropriate because Blender does not permit using modifiers on objects with shape keys, and I really need the shape keys to remain intact for morph animations.
The Shrinkwrap modifier has an 'Offset' setting. If you make one of the surfaces the Shrinkwrap target of the other, projected along target surface normals, with an offset, would that do the trick?