I would like to be able to move the edge of each individual skin in a composite wall at corners and junctions so i can make these clean up in plan view. This would only apply when i have two walls with different finishes coming together at a corner.
This function doesn't exist. Wall skins are meeting and intersecting following Building Material priorities. It works in 99% cases.
In some super specific and complicated cases it is possible to use polygonal walls to build complex intersections.
I know such a function exists in Revit - stretchable wall skins.