Take a look here:
https://derflounder.wordpress.com/2016/12/21/migrating-ad-mobile-accounts-to-local-user-accounts/
It was designed to go from AD mobile accounts to local accounts, but it's possible most of the same process will work for Open LDAP accounts. I can't say because frankly its been a good many years since I've used Mac OS Server accounts on any Macs.
SOLUTION:
1. Objective device must have at least 1 local admin.
2. Login to local admin account.
3. Delete Mobile Account, keep home folder where it is. Don't move it.
4. Go to "/Users" and rename home folder from "username (eliminated)" to "username".
5. Create new local account, it must have the same username. Select the option to "use existing home folder".
6. By doing this all the info still there, the only thing that is halfway lost is the Keychain.
Users will have to login on their office 365, email, and apps account
Petition: If someone can do a script for this issue so it can be automated, it would be great to share.