Yes. If you are on the 'Early bird! 8+' pins tier it's as easy as adding $8 for each additional pin.
If you are on a different early bird tier, you can similarly increase the amount you are pledging to account for additional pins. I recommend messaging me to confirm the price since the price per pin changes at certain quantity thresholds. Messaging me will also allow me to make a personal note so that I don't miss the additions during fulfillment.