Override ContactRequest email

I am using business version of hikashop
There are many email templates in configuration page but there is no for ContactRequest email.

I need to add one addon field - telephone number.
I can do it by changing components\com_hikashop\controllers\product.php file but don't want to do so.

Is there another option to make this?

There is no other option for now. In next version of HikaShop, that email will be editable from the System->Emails menu like the others.