I don't follow.
1. You create a template and add all your networks to it.
2. You create a group policy inside the template.
3. You assign clients to the group policy.
As the group policy is mapped to the template, isn't any client added to the group policy mapped to all networks?
Are you saying that despite having a group policy at template level, you still have to go into each network separately and add a client to the group policy, for the same MAC?