Firstly, not everything can be overriden, sometimes you can just create your own **mod_myk2_tools**.

Secondly, a feature can be overriden only if it is instantiated with a dynamic loading mechanism. This kind of technique checks if a resouse is already loaded before loading, allowing to load it before. In mod_k2_tools module, the helper is just included in this basic PHP way: "require_once (dirname(__FILE__).DS.'helper.php');". *It is not possible to override it.*