Switching UPN\Logon Names is best when replacing a laptop or re-imaging their current machine.
One issue that popped up after distributing laptop:
Because OUTLOOK\WINDOWS accounts is syncing across machines, I noticed that on the new machine with the new LOGONNAME, has cached credentials with the old User name.
In Control Panel, CREDENTIAL MANAGER, under WINDOWS CREDENTIALS, remove any Generic Credentials that have the old username.
Browse to %appdata%\iManage\Work
Delete any files with imanEFSDB in the name
Delete SuggestionsDB folder
Right-Click IMANAGE AGENT in taskbar, restart.
Open IMANAGE WORK in their default browser, open OUTLOOK, check the WORK PANEL, MIMECAST, and CORRELATE. Sometimes, deleting the LOCAL CACHE is necessary.