Getting Smaller Implants - 700cc to 500cc Feasible?

Yes, I have taken care of many patients in your situation. It is possible to downsize and get natural looking results.

 It is very important to communicate your size goals with your surgeon.  In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. I have found that the use of words such as “natural” or “C cup” or "fake looking" means different things to different people and therefore prove unhelpful.

Also, as you know, cup size varies depending on who makes the bra; therefore, discussing desired cup  size may also be inaccurate.
I use  intraoperative sizers and place the patient in the upright position to evaluate breast size. Use of these sizers also allow me to select the press implant profile (low, moderate, moderate plus, high-profile) that would most likely achieve the patient's goals. The patient's goal pictures are hanging on the wall, and allow for direct comparison.
I have found that this system is very helpful in improving the chances of achieving the patient's goals as consistently as possible.
By the way, the most common regret after this operation, is “I wish I was bigger”.
I hope this helps.

Hi Ellie26, Dissatisfaction with the size of one’s implants is the most common reason patients seek a breast revision, almost always switching to a larger implant. But not always! Going down to a smaller implant often requires a Breast Lift (Mastopexy) for the outer breast tissue and a Capsulodesis to make the inner pocket small enough for the new implant size. The old larger scar tissue capsule will also need to be removed.Your case is very doable. My only concern is your focus and specific knowledge on the implant dimensions, but no specifics on the type of lift or internal revision of tissue is needed. You've already had a lift to correct asymmetry and TBD. Going into a third revision you need to know if this is being revised or a bigger lift is needed. These are important details that affect your outcome. Generally your surgeon should be handling the details of relating and utilizing the implant diameter and projection to the relation of your body measurements and existing breast volume. This is a part of the process for an experienced surgeon. Patients are never expected to make a determination on these details in my practice. You simply need to provide your surgeon with a very clear vision of what you want as your outcome and they should be able to tell you what will provide you with that outcome. There are many more variables at play than just the profile of the implant that will give your the size and appearance you desire. Again, they should be providing you with a very clear plan for surgery. The procedures that are needed and what the expected outcomes are from those procedures. (Full Mastopexy, Capsulodesis, Capsulectomy, etc.) Lastly, I will tell you this: Patients focused on a bra size often end up with outcomes they are unhappy with and don't understand why they don't look the way they thought they would.  My best advice is to be concerned with what you look like with a specified amount of volume. What cup size or implant size you end up is really not as important as how happy you are with what you look like. (It sounds like you've already found that out the hard way.) Show your surgeon what you are visualizing for yourself with photos of other patient's outcomes and open the lines of communication. And get a clear surgery plan! Good luck!

A lot of what can be done depends upon your skin quality and the degree of droop or ptosis that you have.  Seek out a consult with a plastic surgeon in you area.  I agree with the person you saw in that many times when you go down significantly in size you may need a lift to tighten the skin around the new implant size. All of this should be possible.
Good luck,
Dr. T