What is the best way to add weight to an arrow without affecting the spine?
Weight tubes.
Also, some arrows, such as Gold Tip, allow you to put weight on both the front and back of the arrow.
Adding weight always affects the dynamic spine, how much depends on where and how much weight you add.
What frassettor said. They are like arrows though place one in the shaft and spin it and rotate it in the shaft untill the shaft spins well without heavey spots.