Following up on this question
I tested the update handle prefix on a 6.x instance and noted
that rather than taking the the entries in the handle column oldprefix/n and replacing it with newprefix/n
the handle_id is used to generate the new handle in the form newprefix/handle_id
This resulted in oldprefix/0 (the sidewide handle) with handle_id 1 being transformed to newprefix/1.
The sidewide handle is used in several places e.g. AIP Backup and restore
Furthermore changing the handle prefix will not affect metadata created with the canonical handle
Maybe this should be better documented.