Thank you for your plugin "Rename wp-login.php".
It works as you designed and has already stopped many Bots on my site. Your plugin is the first I have seen that actually prevents access to the default /wp-login.php which is targeted by many bots.
It works and very well.
I also use another plugin "User Switching" which allows a site admin to assume the user_id of another. We use this plugin often enough to test user permissions and even fix a few things not editable using wordpress.
Unfortunately your plugin disables the "user switching" plugin. The switching plugin is http://wordpress.org/plugins/user-switching/ . It passes GET parms like this ?action=switch_to_user&user_id=323&_wpnonce=123456790.
I diffed your changes of wp-login.php and they look very logical and simple enough. But for some reason it does not work with user switching. The original user switching does not require the administrator to know user passwords and do an new login.
The "user switching" is a popular plugin so I am requesting that you enable you plugin to support it as well.
Thanks for you great plugin!