Hello,
1. There is actually no option to do it, so the solution will directly be to edit the "option" file of the "product" view of your front-end template via "Hikashop->Display->Views" and add such line at the beginning:
<?php $this->params->set('price_with_tax',0); ?>
2. If you followed our documentation here (
www.hikashop.com/support/documentation/i...ct-form.html#options
) and have a characteristic attached to your option, you defined in your characteristic the possible values in the option dropdown, and in the option product, you selected the default value you wanted in the dropdown, so you can just change it there.