Hi,
For what I understand of your request, you will need to create a special override for the product page in order to change how the characteristic selection is perform.
It would use some javascript in order to perform a characteristic selection depending the custom field and also to hide or show the characteristic block.
Like that it will be difficult to guide you for that kind of customization (specially without having details and understanding the all process).
But the customization documentation page will help you to understand how the product page is organized, so you could find the different view that would require an override.
www.hikashop.com/support/support/documen...ize-the-display.html
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.