It depends how much are you planning on changing it - you may have no choice to change the NARD realistically. Say if you were changing it 6 months and doing 18 months accounts;
With the CRO in this case you'd file a B1 with an attached B73 and no accounts. Then another B1 with accounts made up to the new date.
With Revenue you'd simply file a CT1 for 12 months, then one for 6 months apportioning out the results as required (but only including full 18 months extracts with the 1st one), then referring to this in the second CT1.
Again though if you are only changing the accounting period by a month it might be slightly different from CRO point of view (you might not need to change your ARD)