Hi,
There is no option for that.
The label can be changed by adding custom code in the file "quantity" of the view "product" via the menu Display>Views.
You first need to load the characteristic of the current product with a MySQL query on the tables hikashop_variant and hikashop_characteristic.
Then you can easily add the characteristic_name to the label in the line:
Code:
echo $this->cart->displayButton(JText::_('CHOOSE_OPTIONS'), 'choose_options', $this->params, hikashop_contentLink('product&task=show&product_id='.$this->row->product_id.'&name='.$this->row->alias.$url_itemid.$this->category_pathway,$this->row),'window.location = \''.str_replace("'","\'",hikashop_contentLink('product&task=show&product_id='.$this->row->product_id.'&name='.$this->row->alias.$url_itemid.$this->category_pathway,$this->row)).'\';return false;', '');
