Adding onto what Lefty71 said. If your using the same rods and just changing pistons, weigh the new piston, pin, and ring stack. If the weight difference is about 15 grams or less, my advice is no need to rebalance. I've used that method for years on oval track engines that would see some sustained rpm up to 9,000 rpm without a vibration issue noticed, or noticable problems.
I've wondered how far out you could go on a drag type engine that cycles through the rpm fast, before the out of balance becomes noticeable. Just never got brave enough to push it and have a comeback on a job. Maybe someone else on here that has assembled a lot of engines and balances cranks could chime in.
Remember that if your close on weight you have the piston pin weight to juggle around. Buying new pins would be cheaper than the balance cost. Just be sensible with the pin weight and don't use some really light thin wall pin to get there as that piston is a rather heavy slug.