Why do you want to change something that is OOB? This will need to be reviewed during every upgrade and adds a unnecessary maintenance cost.

The roles would usually be added by admins. So I don't see this as a issue causing end user annoyance.

Even if that is the case, I would advise you to stream line your process and build a catalog for adding roles to user instead of doing it directly on the table. This would help in maintaining the audit records for role access and also can be used to automate the process, thus removing manual intervention.