Cabin Upgrade after Final Payment these days

[ew101]

Let's say, hypothetically, there is a good deal on a voyage and I book (probably direct) an inside, and make final payment.  Say 60 days pre-departure, sheltered balconies appear on sale at the inside price.  Do I have any options?  In my experience, booking/paying super early tends to lock a person into higher prices, but is good if you have perks, a specific cabin you love, etc.  

[ew101]

The sale I found features a great fare, and a modest, but non refundable deposit.  The Cunard web booking system refused, steadfastly, to accept either of our loyalty numbers.  The cheerful Cunard 800# desk added them and said they were not optimistic this booking could be altered much under this particular promotion.  I do have a guarantee cabin, so there is perhaps possible wiggle room.  A First World problem indeed.