This should work. Can other users login ok?
What's the error when logging in? If it's a username/password error - then ensure the proper password has been set. If you're getting Access Denied, then you have to give this user permissions to the SharePoint site.
Note that SharePoint matches the SharePoint user profile to the database login based on username - so by changing the username on the database, it looks like a brand new user to SharePoint. If you want to additionally move the user's existing user profile to
map to this username, then look up migrating users in SharePoint.