I am wanting to add weight to aluminum shafts, but it seems to me if I add weight it would change the spine too. Do I need to go up one size on my shafts if I were to add 100 to 150 grains of weight tube ?
I have done it on 2018 and 2117 shafts and saw no real difference in flight, just slower. Weight tubes don't work well in aluminum, they are more for carbons, I tried it in 2018's and they rattle in the shaft. I use rope in mine, depending on how much weight you want to add you can use braided nylon or braided cotton. I have used both. Cotton is heavier.
With nylon I have 29.25" 2018's up to about 600 gr with a 125 gr head. I have the 2117's full length at around 700 gr with cotton with 175 gr heads. I also put cotton in Gold Tip trads and they are at 700 gr. with 175 gr heads.
It's kind of a pain to get the rope in there, but worth it.