Coverting local user to ldap user

I’m currently working on an migration from an old wiki system to xwiki.
In order to recreate all the page structures and the history, I first migrate all the users with a default password. Later I want to connect those users to the LDAP users.
So xwiki’s LDAP extension creates a new “username_1” if the username already in exists.
But in my case I want xwiki just to kind of overwrite that username and using the LDAP Password instead the local default password.
Is there a way to tell xwiki that a local user is now an LDAP user?

Thanks for your help