Shaft MPF is calculated based on the measurements and dynamics of the shaft only. Obviously as dynamics of the total club change, the way the shaft will perform can change, but not as much as you may think. One swingweight added to the headweight is equivalent to 1 cycle, or 1/10th of a flex. Not sure anyone can notice a change of not only the one swingweight point, but 1/10th of a flex. In theory, if you add one swingweight point making the shaft play 1/10th of a flex more flexible, then the shaft would feel and play 1/10th of flex more flexible. More flexible could mean a slightly higher trajectory. Again, one swingweight is not going to be noticeable for most people.