Reducing the volume of implants may not provide the solution you want. You should look at the dimensions of implants (base width, projection) before you have surgery. The projection and width might change by millimeters, which will not be much of a difference in bra size. Fat grafting may provide a better solution for you . You should speak to a surgeon certified by the American Board of Plastic Surgery.
It is impossible to determine if the 50 cc decrease in size implants will be significant. My recommendations are ti provide actual pictures frontal and oblique and obtain the size, shape, profile, and manufacturer of your existing implants.
Those are pretty small implants and it is hard to believe that would make you a "D". Bras do not match implant volumes. Dropping to 125 cc's although is about 30% less may not be much in a bra.
Dear Madison, Front and side view pictures would have been very helpful. Something does not add up, because it is impossible to go from size B to a D with 150-175 cc implants. Either you got bigger implants and you are un aware of it or you gained some weight. You did not provide your chest circumference measurement in inches, which is critical for the correct implants size selection. If you are indeed D cup presently, removal of the implants (assuming they 150-175 cc) will reduce your breasts size by , roughly, one size, which means for you C cup. Replacing them with 100 - 125 cc implants will make very small change. It is best for you to consult with experienced board certified plastic surgeon who can take your chest and breasts circumference measurements and decide with you about the best mode of action. Best of luck, Dr Widder
An exam is needed since you do not provide pictures for us it is hard to give you too much advice. A lower profile implant or possible a shaped low profile implant may be right for your petite frame. Good luck and please update with pictures.