I think updating the server configuration of the existing server, and then do a sync ldap is the way to go. Of course, test it first and make a database backup ;-)
Ok, this rises new questions:
What happens to all associations that I have from entities to e.g. Administration.Account? I assume that System.User/Name is used to map users, or at least is the most preferred way to do so. Will each sync clear the table and add the users again or will it just make the required changes?
When I have two LDAP servers and one mapping per server defined, how are duplicates handled? If a user exists, with the same unique ID (System.User/Name?), in both sources, the second of the two servers wins? Is the order predictable or can it be influenced?
I sync the users with one LDAP server, and when that server is removed from my application's LDAP configuration and replaced by another LDAP server and mapping, are all users from the removed server still in my application and updated with the information that comes from the second server? Assume here that both use System.User/Name as unique key.