As long as you have they don't have any more than 10 SAS-based disk shelves in any disk stack connected to the SAS ports, you should not have to "rebalance" the disk shelves.
I have provided the link for the "Universal SAS and ACP Cabling Guide" for your review which contains the best practices for cabling the shelves to the SAS ports on all NetApp FAS controllers.
https://library.netapp.com/ecm/ecm_get_file/ECMM1280392
If the they are wanting to still redistribute shelves, then I would follow the universal guide and balance out the shelves across all the available port. As always, contact NetApp support and create a ticket before doing any moves just to have support ready in case they run into trouble.
NetApp Global Support Center: 888-4NETAPP (888-463-8277)