Thinking of changing 1000cc implants to 800 cc silicone

It is certainly feasible to #downsize to smaller implants and also alter the positioning; if possible. However, #decreasing is size may also require a Breast #Lift to to #tighten loose skin, better optimize the end result. Any #revision has risks of unhappy outcome or other complications. Also, the right implant for the revision is contingent on shape of body and your desired outcome. Another element to a satisfying result of your #augmentation is realistic #expectations.Talk to your surgeon at greater length and be sure to view before and after pictures and reviews beforehand to gain more reassurance of the procedure.

Thank you for the question and pictures.  Yes, If you were to downsize your breast implants, it is likely that  your breasts will look "more natural" but still be large. Whether or not 800 cc breast implants are the correct choice, I can not tell you based on the limited information online.Keep in mind as you are thinking about your goals that sometimes adjustment of the breast implant pockets (capsule adjustments) may be necessary to achieve the outcome you are looking for. Much will be dependent on your physical examination;  specifically, factors such as the amount of redundant skin, quality of skin elasticity,  and how much you choose to downsize will be important.
Generally speaking, the best online advice I can give to ladies who are considering revisionary (downsizing) breast augmentation surgery is:
1. Concentrate on choosing your plastic surgeon carefully. Concentrate on appropriate training, certification, and the ability of the plastic surgeon to achieve the results you are looking for. Ask to see lots of examples of his/her work.
2. Have a full discussion and communication regarding your desired goals with your plastic surgeon. This communication will be critical in determining breast implant size/type/profile will most likely help achieve your goals. 
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 and large” or "down a cup size” etc 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. 
3. Once you feel you have communicated your goals clearly, allow your chosen plastic surgeon to work with you in determining the best plan to achieve your goals.
I hope this, and the attached link (dedicated to larger breast augmentation surgery concerns) helps. You will find a separate page, on the same website, dedicated to downsizing revisionary breast surgery concerns. Best wishes.