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

Going down by about 100cc should not require any type of lifting surgery.  The implant selection should be based on a combination of your desired size, soft tissue dynamics, breast base diameter and skin elasticity.  I recommend an in-office examination as well as a detailed discussion with a surgeon who you are comfortable with.   Finally, make sure your surgeon is a Double-Board Certified Plastic Surgeon certified by the American Board of Plastic Surgery (ABPS), a member of the American Society of Plastic Surgery (ASPS) and the American Society of Aesthetic Plastic Surgery (ASAPS).Best,Dr. DesaiBeverly Hills Institute for Aesthetic Plastic SurgeryHarvard Educated, Beverly Hills & Miami Beach Trained, Double-Board Certified Plastic Surgeon

Most likely you will not need a lift if you are going down the amount you describe. You will end up being a "smaller version" of what you are now.
Lifts can always be done later, at no risk. You don't have to have scars from the lift at this time. If you do need the lift in the future, second procedures can be safely done.
The biggest risk of going smaller is missing the fullness you have now. You lose it from the "top" of the breast. If you are confident that this is the size change you want, in my experience, patients are usually very happy.
Hope this helps!
Dr Chris Saunders 

When downsizing implants, some patients will benefit from a mastopexy (breast lift). This depends on: --how much, if any, droop is present, --how much the implant size decrease/increase will be, --what the quality of the breast tissue and skin is like,--and what your goals are as far as size, shape, etc.  The incisions are generally a worthwhile tradeoff for improvement in the breast shape. The type of lift depends mostly on how much droop you have. Also, it is very important to alter the breast implant pocket if needed. Most often with implant downsizing, a capsulorraphy (making the pocket smaller with internal sutures) is needed. This is essential to place the new implants in the proper place to give nice contours. Good luck. Take your time to find out what is best for you. 

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. 

With downsizing, you may need a lift. You would have to be seen in person to be properly evaluated.  Best of luck.

Just because you are going smaller does not necessarily mean you will need a lift. I would need to see photos of you to give you a more precise opinion. It really depends on how much skin laxity you have and what your goals are. Best of luck.

 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.