Hello,
To empty the field, it requires to override the product edition view and remove the value from product object when it's a creation.
Afterwards, it is complicated to make the field mandatory since there is some checks in HikaMarket to fill the field if that field is empty (using the current browsed category or the vendor category)
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.