Going from 650cc to 400/450 cc

When downsizinig, there is always a concern of having an excessively generous envelope. If your implant dimensions are dropping considerably in width, its likely you would benefit from tightening up the pocket at the time of your procedure and after the implants are in, then and only then can you determine if a vertical plication of the mound would be beneficial to the outcome. Your nipple doesn't have to be moved but a vertical plication could make your lower pole a lot more snug and round rather than droopy. Or you could simply do as your surgeon says, hope for the best and then return later if you have issues.

Downsizing implants after weight loss often helps tremendously with not only the appearance but the side effects of the weight of the implants. Hopefully you will experience some improvement in any neck, back, or shoulder discomfort you are having. After the smaller implants are placed, there will likely be some excess skin. Depending on the elasticity of your skin, there should be some skin contraction over time. Just how much skin contraction you will get is very hard to predict. You could go with your surgeons recommendation and wait the 4-6 months after surgery to see the final result and always go back for a lift down the road if you are trying to minimize surgery. On the other hand, doing the implant exchange and lift under the same anesthetic could get you to your desired goal faster and with one less trip to the operating room. Best wishes on a speedy recovery and great result.