gistfile1.txt

if ( !class_exists( 'HijackMe' ) ) {
    class HijackMe {
        public function hijack_menu($objects) {
    		/**
		 * If user isn't logged in, we return the link as normal
		 */
		if ( !is_user_logged_in() ) {
			return $objects;
		}
		/**
		 * If they are logged in, we search through the objects for items with the 
		 * class wl-login-pop and we change the text and url into a logout link
		 */
		foreach ( $objects as $k=>$object ) {
			if ( in_array( 'wl-login-pop', $object->classes ) ) {
				$objects[$k]->title = 'Logout';
				$objects[$k]->url = wp_logout_url();
				$remove_key = array_search( 'wl-login-pop', $object->classes );
				unset($objects[$k]->classes[$remove_key]);
			}
		}

		return $objects;
	}
    }
}

$hijackme = new HijackMe;

add_filter('wp_nav_menu_objects', array($hijackme, 'hijack_menu'), 10, 2);