I'm trying to change the URL path for grader/lib.php overriding parent class constructor.

I have extend grade_report_grader and override $this->pbaurl but nothing happens.

class my_grader_plugin extends grade_report_grader {

      public function __construct($courseid, $gpr, $context, $page=null, $sortitemid=null){

          parent::__construct($courseid, $gpr, $context, $page);

          $this->pbaurl = new moodle_url ('/grade/report/myreport/index.php', array('id'=>$this->courseid));

     }

}