Title. I'm not sure that is supposed to happen, but both SRB-A and SRB-U don't get their costs updated by changing the parts' sizes (diameter or core). If this is supposed to happen, consider this post an improvement idea 😄

it also didn't change the max fuel if you change the size, so i think its fair not to change the costs :D

Edit: Not changing the fuel capacity, seems to be a mod conflict with RealPlume