I have a though but don’t know if it will work.
1. Execute an SQL query that will write the md5 of the passwords to the moodle database. We have the password as we gave it to the clients and as far as I know they can’t change the password stored in LDAP.
2. Change the records of the user table from LDAP authentication to internal. I su
Any ideas if this will work or any other ways to do it?
as far as I can tell, that should work, provided you create the MD5 of the passwords with the right salt (if you are using $CFG->passwordsaltmain -- see validate_internal_user_password() in lib/moodlelib.php).
One final note. The name of the internal authentication plugin is actually 'manual'.