Allowing users to change their own OpenIDs

I wrote a function that allows users, including those that are already registered, to choose their OpenID.

It's not the perfect solution. Three further developments would include:
1 - Create permissions that either allows or not the user to change their IDs
2 - Like Wordpress' OpenID plugin, make obligatory to user to confirm identity before registering it
3 - Allow Drupal user to be linked to more than one OpenID

Anyway, by now it's already quite useful.