How to change the default notification_preference value for supplier?

I know we can change the notification_preference for user on the preference page, but how can we change the value for supplier? we found in table wf_local_roles, the notification_preference value always default to MAILHTM2, which prevent supplier to get the mail attachment, where can we change it for supplier in front end? or can we change the default value to MAILHTML when creating/synchronizing record in wf_local_roles?