Omeka classic , modify add input

Omeka Classic
1

class MyPlugin extends Omeka_Plugin_AbstractPlugin
{

$_filters = array('relabelItemTitle' => array('ElementForm', 'Item', 'Dublin Core', 'Title'));

public function relabelItemTitle($components, $args)
{
    $components['label'] = "Label";
    return $components;
}

}

to edit elementform , where should i put this code , to determine wich "Add input " button delete ( coverage or item or anyone ) in admin page , is it in the elementform.php file or in globas where the functions are defined?