class Controller_Template extends Fuel\Core\Controller_Template { // ... }And add it to the Autoloader::add_classes section in your bootstrap.php. See http://docs.fuelphp.com/general/extending_core.html for more details on that. If you do it that way, you can still use "extends Controller_Template" in your controllers, and they will automatically use your modified one instead of the Fuel core one.
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