CREATEUSERWIZARD or OWN REGISTRATION TABLE

Question

I am creating an Employee Site for employees to insert their CV and employers to contact them.
I have 3 main tables:-

1. Employee_Career_History (career_id, username, experience, area etc.)
2. Employee_Education_Details (edu_id, username, qualification, details etc.)
3. Employee_Hobbies (hobby_id, username, hobby etc.)

Suppose an employer wants to see the details of a PARTICULAR employee, at the button click event of the search button, I run a query like-
"select * from Employee_Career _History where Employee_Career _History.username=@username"
Now, the problem is-

1. if the user CHANGES HIS USERNAME, his record in the tables will never be accessed by the employer when he wants to see that particular person
(because the employer sees his new username and in the record in table has ONLY his OLD username), so
should I go some other key (eg. ProviderKey) or Should I go for myown registration table instead of createuserwizard?
2. Will CreateUserWizard in asp.net allow to CHANGE USERNAME?
3. I am using email as the username (in the text box for username I ask the user to enter email id). Hope it is fine.