I would keep trying. Things do open up when you're there. Your hotel concierge if you're on site will also help if you ask.
As far as max capacity, it really doesn't happen that there's openings. It CAN, but I would not expect it. We've seen people constantly there arguing with the CMs in the front of several restaurants and they just do not get in. There's way more people hoping to get in, than people who don't show. And for some reason last year I kept seeing people book reservations for 2 and then trying to get 3-4 people in. They did not get in most places and if they did, they were told the wait was an hour or more with no guarantees. We even wondered since there were so many if a site or book wrongly told people it could happen. The one exception is Tusker House who always tries to accommodate.
Don't forget also that there are CL guests and on site concierge CMs who are constantly checking in case some one doesn't show up for their other guests (and with a $10 per person charge there's not many no shows especially for hard to get reservations like CRT and BOG), but I wouldn't show up expecting to be accommodated with an extra few guests. I'd be sure to keep trying to change the reservation to the right number.
My mom last year two months or so after our 180+ and all our ADRs were made decided to "come along" with us. Great, right? It was a nightmare. For me. I can laugh about it now, but I still don't think she has a CLUE the chaos she caused and how lucky we were that they were able to include her in our
free dining deal and deluxe upgrade. There were several reservations I could not add her to at all and had to start over completely. CRT was one of them even after speaking directly with the restaurant and several CMs trying. And this was for 4 instead of 3 so they couldn't add even 1 to a 4 top! They explained it was more the firecode and aisles to keep open to consider and an infant counts in both the count and keeping the exit clear so there's not much "oh just throw a high chair on the end." Especially at CRT where not only the waitstaff have to be able to move around with big trays of hot food, but the other guests, and princesses.
(And then after all that work my Mom was exhausted from all the walking and started skipping meals to hang out in the room.

)