this really looks like a promising plugin, but it didnt work for me, cause it blew some other plugins that builded their own custom links (my shop stopped working properly) so i guess it would be cool, to have the option to choose, which post types should get a custom link.
plus i found an error. when using %author% your function is still wrong, cause it grabs the user name, not the user url
$user = get_userdata($post->post_author); $newlink = str_replace("%author%", $user->user_login, $newlink);
$user = get_userdata($post->post_author); $newlink = str_replace("%author%", $author->user_nicename, $newlink);
plus, but i dont know if this is solvable:
when creating a new article and you enter the title, the url gets generated. but without the replaced %author%. you first have to save, to get the correclty rendered url. but this aint too important.