Hi,
You can do that but it require a specific "process".
First, you have to remove the "default value" and also remove the option "required".
It will allow you to save the custom field and remove the default value in the same time (because if the field is required, you can't "no set" a default value. We will fix it in a future release, it's in the TODO list).
Then you can re-set the "required" on the custom field (and let the "default" empty).
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.