I'm very happy to read you're getting all your deposit money back.
When booking cruises this far in advance, over 6 months as was in this case, it's a good idea to figure out when the ship's next drydock is scheduled.
Evey cruise ship drydocks every two years for general maintenance and to maintain their certifications. If you don't see a two week break in the ship's schedule every two years, your cruise may be cancelled for a drydock at any time.
It was in the Spring 2004 when the POA last had a drydock, when the ex-Sky was remodeled into the POA. With that knowledge, an informed cruiser should have known that the POA had to have a drydock sometime during the Spring of 2006.
Drydocks are usually scheduled six to nine months in advance. Wait to book your cruise unto you discover when the required drydock is scheduled.
The problems that occured in this case was (1) you booked your cruise on a ship before NCL scheduled a drydock and (2) having to switch ships, and the ships aren't sister ships with the same number of cabins in each classification. The POA has 427 Inside Cabins, 572 Outside Cabins, 257 Cabins & Suites w/ verandas, and 14 Suites. The ship assuming additional passengers, the POAm has 229 Inside Cabins, 846 Outside Cabins, 706 Cabins & Suites w/ verandas, and 52 Suites.
You could probably still sail on her on near your selected date if you were willing to upsell to a higher class cabin. The POAm has 198 less Inside Cabins than the POA, there's no way it can assume all the POA Inside Cabin passengers on one sailing.
I'm sorry you can't be flexible with your vacation plans due to circumstances outside your control. I hope you find an alternate vacation for this May which you'll enjoy. Hopefully you will be able to reschedule another vacation and cruise to Hawaii soon.
"Mama always said life was like a box of chocolates. You never know what you're gonna get." Forrest Gump