Ahoy there, Lisa!
Thank you so much for sailing by planDisney with your 
Beak and Barrel question! What an exciting time to be visiting Magic Kingdom —the holidays are such a magical season to see Main Street, decked out in its festive finery. And shiver me timbers, a reservation at Beak and Barrel is quite the treasure to snag! I was lucky enough to dine there recently, and let me tell you, it’s a pirate’s paradise from bow to stern—filled with laughter, lively crew members, and just the right amount of mischief on the menu.
Now, let’s chart a course for your question! Once you know your final party size, that’s the perfect time to modify your reservation. It’s always easier to adjust from a larger crew down to a smaller one than it is to add more scallywags later on. So I’d recommend waiting until you’re sure your ship’s roster is final before making changes. This helps the Cast Members prepare the proper table for your crew—especially for a reservation as popular as this one!
To modify your reservation, simply open your 
My Disney Experience app, tap Future Plans, locate your Beak and Barrel reservation, and select Modify. From there, you’ll be able to change your party size and follow the prompts to update your plans smoothly.
While you’re there, don’t miss a chance to try the 
Kraken’s Catch or the Island Provisions—they were the crown jewels of our meal! And be sure to soak up the lively pirate atmosphere. The Cast Members here truly bring the adventure to life—you never know when a playful pirate or two might appear to join your crew!
Lisa, I hope this helps you navigate your dining plans with ease. Wishing you smooth sailing, hearty laughs, and a jolly good time at Beak and Barrel. If you have any additional questions, feel free to visit us again. 
See ya real soon,
Christina