Custom user login in Facebook Auth modules
Provided that you're using v8.3 or higher of the module, a possible solution would be to create a form where the user decides which values are stored according to his/her needs and your requirements of course.
Then, using the provided events in the module, you can redirect the user to this form which will accept the $user object and apply the changes accordingly.
You should add an EventSubscriber service which listens to simple_fb_connect.user_created event as per the module documentation linked above. Thus you're only showing this form to the user once after the account has been created and not with every login.
Hope this helps.