You'd need to change like 1 thing through phpMyAdmin.
Go into the database, find wherever the **** the user options are stored (I'm guessing users) and change the default value for new entries.
Far as I know, it doesn't take anything from any HTML forms at sign-up, so it's just using the default value set for that field in the database.
And if you really wanted to put things right, you could redo the entire field and set it to the new default value. Just delete the field and recreate it with the new default value. Then it'll change everyones and no-one will have to *****.