Hi,
I think it can be done using "item custom field".
www.hikashop.com/en/support/documentatio...p-field-listing.html
With the item custom fields, you will be able to personalize the information you can gather from your customers when they order something on your store. The custom fields will appear on the products page where you will be able to ask the user information related to the product he wants to buy. It's useful when you sell personalized goods like for example a shirts selling website where the customers can upload an image to be printed on the shirts. This is only available in the business version of HikaShop.
For the registration, HikaShop add a message using the translation key "THANK_YOU_FOR_REGISTERING".
You can create a language override in order to set your personalized message.
www.hikashop.com/en/download/languages.html#modify
Regards,