You can feed and water your birds and remove poop. The only time you are not allowed to handle or mess with your birds is when the judge is on the aisle. Even if your birds are the only Brahmas they are only eligble for BV, a non-recognized variety can not be BB. BTW You can coop in early on the day of the show. Judging typically begins at 9am, so your birds need to be cooped and groomed by then. The first time I went to a show I had NO IDEA what to do. Believe me, everyone has been there and everyone is more than willing to help you in any way they can. Chicken shows are the greatest thing. After a while the winning and losing are not the main thing. You get to meet people who love Brahmas as much as you. You get to "talk chicken" all day. Some of my best friends are people I have met through showing. Try it, you will like it!!!
Tim
Yes checking in the night before is best. You will find the show secretary and everyone to be ready & able to help you get your birds cooped in. And I would recommend joining the local poultry club nearest you. When I joined my local club United Poultry Fanciers back in 97, I met Art Rieber

between the monthly club meetings, poultry clinics put on by the club, and Art's mentoring, I went from clueless newbie to APA master exhibitor at warp speed lol ... I second Tim's advice, try it, you will Love It.