I want that in one of my groups users can post anonymous, for example in a group with guid=61. Is it possible???

I try this in topicposts.php, but it does not work like I want:

if ($group_guid = 61) {
      echo "<div class=\"post_icon\"><img src=\"" . elgg_view('icon/user/default/small') . "\" /></div>";
                           echo "<p><b>" . elgg_echo('Anonymous) . "</b><br />";

 } else {

                        //get infomation about the owner of the comment
                        if ($post_owner = get_user($vars['entity']->owner_guid))  {
                        
                         //display the user icon
                         echo "<div class=\"post_icon\">" . elgg_view("profile/icon",array('entity' => $post_owner, 'size' => 'small')) . "</div>";
                        
                         //display the user name
                         echo "<p><b>" . $post_owner->name . "</b><br />";
                        
                        } else {
                         echo "<div class=\"post_icon\"><img src=\"" . elgg_view('icon/user/default/small') . "\" /></div>";
                         echo "<p><b>" . elgg_echo('profile:deleteduser') . "</b><br />";
                        }

   }

 With this code it shows me in all groups anonymous instead of the username. But it should be only in the group with guid=61.