Breast implant reduction from 400cc to 275 or 300cc: Does this require scarring other than around my current areola scar?

 Keep in mind as you are thinking about your goals that sometimes adjustment of the breast implant pockets (capsule adjustments) and/or breast lifting may be necessary to achieve the outcome you are looking for.   Whether or not the adjustment of the breast implant capsules or breast lifting will be necessary will mainly be dependent on your physical examination; specifically, factors such as the amount of redundant skin, quality of skin elasticity,  and how much you 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” or "down a cup size” or "C or D cup" 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 revisionary breast surgery, specifically downsizing breast augmentation surgery concerns), helps. Best wishes.  

Reducing the size of an implant especially if it is under muscle should not require a lift (scars) unless you originally had droopy breasts.  It may result in some flatness on the top, however. Best to see a plastic surgeon who will examine you and give you the best advice after the examination.