Hi,
The user custom field is always editable.
If the custom field is not displayed in the front-end, it won't be editable by the user.
The solution could be to override the view in order to change the way that the custom field is displayed, not put the classical input (but display the content and let the value in an hidden input field).
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.