Could anybody please point me to the location a of script or some
setting which controls the change of the group when the new home
directory is created (owner is fine and permissions are not being
changed)? If it is possible to customize this right during the
creation process at all.
I don't know where this value resides, however, you could add to your
client a LoginHook which would create the necessary folder when the
user opens its first session, then deletes itself.