User_login and email address

Hi. I’m wondering if you can help me understand a couple of things.

I have imported users successfully, and the usernames I imported were just firstlast names.. however, when people created a new user, I had the setting set to autocreate usernames initially in wp. (changed that now). The problem was duplicate users were being created because usernames were different since when woo user registration creates, it created usernames with first.last which is different from what existed creating a duplicate user.. so i turned that off..

Can I edit the user_login field to be email addresses and have it update? or will the email address mess things up..?

Thanks