Migrate from 7 character user-ids in LDAP to 8 character user-ids
3 answers
What you want to do is to change the user ID from the existing users and not create new users with new user ID's. How this can be done is explained here: https://rsjazz.wordpress.com/2012/10/12/changing-the-jazz-user-id-using-the-rtc-plain-java-client-libraries/ - please note that this is not supported by IBM at the moment, you would do this on your own responsibility. Backup your data and test this on test systems.
This way, everything would be as it was, the users would be the correct owners and all links etc would stay correct. There have been issues in some applications e.g. doors next generation as mentioned in the blog. In newest versions these might be solved.
I would suggest you contact support to get their opinion on the version you are running and if they see issues using the user ID change procedure.