Importing Linkedin Profile for existing users

Not yet. We've already received this request, and are planning a few ways to do what you're looking for over the next month (or so):
1) A "Import Profile" button that can be added on your site (like the User Details page) or other places. This will let the user automatically pull in their profile whenever they want.
2) Another checkbox on the left hand side of the Login/Register page for connecting to an existing Joomla account that will let the user login to that account and update their profile.

We're going slowly with some of the profile import stuff because LinkedIn's Terms of Service state that a user has to explicitly choose to import their profile information. For our Facebook Connect component, we have options to automatically pull in the profile on every login, but can't do that with LinkedIn, so are trying to find good solutions to exactly what you're looking for above.

Hope that helps, and thanks for the feedback!
Alex