If done while the server is off, the array will not need to be rebuild ... the controller is smart enough to know the drive's place in the array, regardless of the physical slot it is attached to. If done while the server is on, the disk will become out of sync with the others and will need to be rebuilt into the array.
What I mean is with the server powered off can I move the drives to different slots and will the Raid controller simply know which drives are which without any reconfiguration.  Reason we want to do this is to separate Raid 1+0 drives across the two SAS channels to ensure resilience if one channel fails, the layout being: 4 - disk Raid 10, S=Stripe, M=Mirror, Assume machine is delivered as:Slot 0 - S1MaSlot 1 - S1MbSlot 2 - S2MaSlot 3 - S2Mb To ensure resilience we want to change this across both SAS-A and SAS-B channels:Slot 0 (SAS-A) - S1MaSlot 1 (SAS-A) - S2MbSlot 8 (SAS-B) - S2MaSlot 9 (SAS-B) - S1Mb That way is either SAS-A or SAS-B fails the array is still functioning. 
Are Raid drives identified by an ID or by physical slot?