Hi,
If you just want to change the text of the button, it can be done without a button template override.
You can change the code :
echo $this->cart->displayButton(JText::_('ADD_TO_CART'),'add',$this->params,$url,$this->ajax,'',$this->row->product_max_per_order,$this->row->product_min_per_order);
in the file "quantity" of the view "product" via the menu Display->Views.
But that still requires some programming skills to load the category of the current product and change the JText::_('ADD_TO_CART') based on the category...