If you are externally balanced already, and you get lighter Pistons you'll need to remove weight.
Depends on who does it, but when I have the option I take the weight out of the external parts of the balance job and not the crank. The less external weight you have to use the better IMO.
You can also take the weight out of the counterweights. Who knows...you get it light enough, you may be able to make it an internal balance. Just need to get it up in the machine and see what it looks like.
