I'm not entirely sure if I'm wording that right, so I'll try to explain a little better. I have a solidify modifier applied to an object with the rim and shell marked as their own vertex groups. I want the vertex groups to have a different material than the rest of the mesh, but the only way that I can think of doing that is to apply the modifier and assign the material the regular way, which is destructive. How can I assign the material to the vertex groups without applying the modifier? Is there maybe a node that can assign materials to specific vertex groups?
In this case, the modifier provides a Material Index Offset setting for generated geometry.. (just above the Vertex Group assignments) so you don't need any get-arounds..
(This circle is solidified downwards, from red to blue)
In general, until a node is provided, this method by @Nathan can get vertex-groups / weights into shader trees.