Replace Abstract Class with Interface - php

Question

I'm working on forking an existing MVC PHP application and all normal page controllers are extended from controller.
class MyController extends Controller
The controller class is an abstract class with 2 magic methods, __set and __get and a constructor __construct
abstract class Controller {
protected $registry;
public function __construct($registry) {
$this->registry = $registry;
}
public function __get($key) {
return $this->registry->get($key);
}
public function __set($key, $value) {
$this->registry->set($key, $value);
}
}
I've searched all through the entire application and nowhere are __get or __set ever called manually. So I have to assume that these methods are indeed magical and are doing something with the registry that isn't available to see.
Dispatching is done through the Front class which already holds the registry as an object:
final class Front {
private $registry;
private $pre_action = array();
private $error;
public function __construct($registry) {
$this->registry = $registry;
}
public function addPreAction($pre_action) {
$this->pre_action[] = $pre_action;
}
public function dispatch($action, $error) {
$this->error = $error;
foreach ($this->pre_action as $pre_action):
$result = $this->execute($pre_action);
if ($result):
$action = $result;
break;
endif;
endforeach;
while ($action):
$action = $this->execute($action);
endwhile;
}
private function execute($action) {
$result = $action->execute($this->registry);
if (is_object($result)):
$action = $result;
elseif ($result === false):
$action = $this->error;
$this->error = '';
else:
$action = false;
endif;
return $action;
}
}
My thought was that replacing the abstract class Controller with an Interface would be a better solution, but I'm unsure about what these magic methods are actually doing.
How can I tell if I can/should make this change?