I would avoid doing it online if possible. It will change disk names, and it was reported to cause issues.
If you absolutely must do it online, open case with netapp and try to assure support and get step by step action plan. It could work if you disable paths through lower bridge and let filer "forget" about them completely; but I'd double check with netapp.
Disks on ATTO bridge are named <slot><port>.<loopID>L<LUN>; the <LUN> part enumerates disks starting with the shelf to which ATTO bridge is connected in physical order of shelf attachement (for each side A and B). If you change shelf order in a stack, disks get different LUN numbers. It is not a problem for offline change; but for online - who knows. I appreciate if you could post support response.