Is your 4TB drive failing or questionable, or are you just wanting to upsize?
Parity swap isn't necessary for healthy disks, you can just replace parity, then after parity is rebuilt, just replace the data disk with the former parity disk and let it rebuild.
You might still want to do it the parity swap way, but just be aware that your array is offline during the parity copy part of the procedure, since parity cannot be allowed to change while it is being copied.