hmmm, I see. Thanks for your reply.
The reason I wanted to have username the same as emails is to make user upload easier. I'm enrolling students in multiple courses using user upload function and by default Moodle is using username as a user identifier, means that when I generate CSV file with a list of students and respective courses from our student management system I need to add Moodle usernames to that CSV file to be able to enroll students in courses in Moodle. So I thought if it's possible to make username the same as email then it will reduce the time on adding username from Moodle, because our student management system has only student emails as ID and cannot communicate with Moodle to get usernames.
Is there any other way of bulk enrollment to multiple courses where I can use email as user identifier?