RE: .54 caliber Minnie Balls
If you want to try to "tweek" your mold to increase diameter, you don't have much to loose with lee molds because of the price. Two ways to increase diameter.
1. Get some aluminum duct tape, the type with the paper backing. Cut two strips the length of the mold block height, and use them to shim the mold halves. Sounds strange, but it works, and it will not make out of round bullets until you increase the space between blocks more than the tape will do.
2. Cast a bullet, and imbed a nail or metal rod in the center of it. Coat the bullet with lapping compound, and chuck it in a drill. Go slow and easy, and you can increase bullet diameter several thousandths iwth that process as well.
Tape is a quicker fix, but some would rather lap the mold. Your choice.