Can I see the ItemInit?
Edit: oh I just noticed what you're doing there. That would be your ToolInit if I'm not mistaken, right? So, to achieve what you want to do you could create the ToolInit which should not extend anything and implement the deferred register in it. Then create your own class of the item and instead of doing new Item or AxeItem you do new YourClass. The class we're talking about should extend the type of item you want to imitate, in this case it seems it's an AxeItem. So YourClass extends AxeItem. Then in that class you override appendHoverText and write stuff inside it.