I've searched the forums and I think I've determined that it is possible to change the name of a plugin in the repository, but not the URL in the repository, so it will have the old name as the URL.
I'm okay with that, it's not preferable, but better than making a new plugin listing I think. The thing I am wondering is what will folder name and zip file name be? Will it be the plugin name, or the original plugin slug? And will it make any difference inside the plugin? All my file references are using some form of plugin_basename( __FILE__ ), so I'm hoping they will be suitable no matter the folder name.