What about the inside? What changes are there? No plot changes at all. The only big cuts were in repeating dialogue from "Pride and Prejudice" except what changed because of the events in the book. There was also some good editing where I tend to get too wordy or parts that didn't add in any way to the story. So if you already own "Pemberley's Promise" you won't miss out on anything from "Darcy's Voyage" if you don't buy it. But then, I certainly won't stop you if you want to buy this one, too!
Whether you own the "original" or decide to buy this one, I hope you like the cover, the title, but most of all, the story of Elizabeth and Darcy meeting aboard the ship, Pemberley's Promise.