The biggest problem that a tournament director has with kids changing weights at weigh ins, at least that I have seen, is the time needed to change all of the brackets, bout sheets, mat assignments, allotted time between matches, and other intangibles. Just last weekend, at the Derby tournament we gave ourselves an hour to make bracket changes after the morning weigh ins to account for any scratches. we had a system down that worked very well and we were able to start the tournament pretty much on the time that we stated on our flyer. This is one of the main reasons that tournament directors dislike making weight changes at weigh ins because of the time involved, and we all have been to tournaments that have started 1, 2, sometimes even 2 1/2 hours late due to bracket changes being made. A wrestling tournament is long enough without having to wait that extra bit in the beginning to get things started.
Also, most local tourneys will have a night before weigh in as well as the morning weigh in. If you are not travelling a long distance, try to make the night before's weigh in. I know when we travelled down to Blackwell this year I took 5 kids with me to weigh in the night before the tournament just so we didn't have to get up so early in the morning to weigh in.