Seabourn is essentially your travel agent here, they should have gotten notified of your schedule change and asked you what you wanted to do. You indicated you called Delta and now have a rebooked option that is less desirable, yet you agreed to it. Is there any option to call Seabourn directly and see if you can re-book the re-book? Even if it's a cruise bulk-fare, they may have some other options that aren't going to charge extra for.
If you legitimately miss a connection due to IROP, KLM's auto-rebook system may pick Y seats on the most direct (quickest) new routing option, but I agree with MSP above, you ought to be able to decline that in favor of later options with your paid class of service.