That will work and is probably faster than what I was doing which was dragging and sliding on the translate values while watching a progressive render.
When you paste your values it's better to paste them into the instance of the material in the group rather than in the original material.
As far as I know, there's no way to apply a material to a group while in an Action (or a Pose) like you can a decal. That would very powerful if we could distort a model in a pose and apply a material.
I don't think placement is important for matcap since it doesn't have 3D details like combiner materials do. Let me know if I'm wrong.