In order to migrate users to the new cluster and not destroy access to the old one at the same time, both webservice and maintain-kubeusers (new and old editions) must be capable of shifting a tool to the new cluster and, ideally, back.
One way to accomplish this is to merge the kubeconfigs in both editions of maintain-kubeusers. Then webservice and kubectl can simply set the correct context, allowing smooth migration in either direction.