I installed/activated the plugin and copied the "feed-" php files from the wp-includes folder. So now I just edit the php code of those files to my heart's content? So what exactly does your plugin enable be to do? Just to check, I deactivated your plugin and I can edit those files in the appearance editor in exactly the same way, so I don't notice that this plugin actually does anything at all.
Please tell me I am missing something.