But it should work just fine, just be sure to stop the binhex docker and wait a little bit and try to register the emby/emby docker.
Or you simply make a post on the emby forums that you want to migrate to a new docker and your registration key doesn't work, but I think you have to wait at least an hour or so to "release" the key.
Eventually @binhex can help, eventually there is a dependency missing in his container or something else, so you don't have to migrate to a new container.