You may want to pull in you local NetApp resource to help out.
It may not hurt to open a Case with support either!
If you followed best practices when setting up your LUNS, you should have at least two BLOCK LIFs on each of your 4 controllers.
You can go into advanced mode.
Shut down one LIF on node 1, modify the LIF port to be on node 5. Bring the LIF back up.
Shut down one LIF on node 2, modify the LIF port to be on node 6.Bring the LIF back up.
Shut down one LIF on node 3, modify the LIF port to be on node 7.Bring the LIF back up.
Shut down one LIF on node 4, modify the LIF port to be on node 8.Bring the LIF back up.
Now you should have one active LIF on every node. You may also have to modify your LUNs to expose all paths (reporting nodes). Normally, SLM (Selective LUN Mapping) is on and only advertises the node where the LUN is plus the HA partner paths. I suspect you can also modify to only advertise the paths you would like (like 1+2 and 5+6 in my example).
Verify the client sees the paths.
After that, move LUNs from node 1 to node 5. You should see the active path flip from 1 to 5.
Repeat for LUNs (1->5, 2->6, 3->7, 4->8)
Verify clients still see the paths.
Now:
Shut down the second LIF on node 1, modify the LIF port to be on node 5. Bring the LIF back up.
Shut down the second LIF on node 2, modify the LIF port to be on node 6.Bring the LIF back up.
Shut down the second LIF on node 3, modify the LIF port to be on node 7.Bring the LIF back up.
Shut down the second LIF on node 4, modify the LIF port to be on node 8.Bring the LIF back up.
Modify the LUNs reporting nodes as needed
Verify clients still see all paths.
I have not fully detailed steps here on purpose. I am expecting you to do at least a little bit of searching through docs.netapp.com and support.netapp.com to better understand the steps, like looking up reporting-nodes.
Here are a few links to get started.
https://mysupport.netapp.com/site/article?lang=en&page=/Advice_and_Troubleshooting/Data_Storage_Software/ONTAP_OS/How_Selective_LUN_Mapping_(SLM)_work...
https://docs.netapp.com/us-en/ontap/san-admin/move-san-lifs-task.html
https://docs.netapp.com/us-en/ontap/san-admin/selective-lun-map-concept.html