Quick Create (Change Assigned To...)

Found a solution, I used jquery instead. I put it before the return $str on the display() function of the file: root/include/EditView/EditView2.php

  if($this->returnModule == 'Accounts' && $this->module == 'Opportunities') {
     $data = BeanFactory::getBean($this->returnModule, $this->returnId);
     if($data->id) {
        $user = BeanFactory::getBean('Users', $data->assigned_user_id);

        $str .= "
        <script>
           $(function() {
               $('input#assigned_user_name').val('{$user->first_name} {$user->last_name}');
               $('input#assigned_user_id').val('{$user->id}');
           });
           </script>";
       }
   }

This will only work on Accounts detail view Opportunities subpanel