Ways to reduce breast size for keyhole/ peri areola top surgery?

There are several methods used which depend upon the patient’s breast or chest #size before surgery. Considerations include the #laxity of skin, the #size of the #areola, the amount of #fat and recent weight #gain or weight #loss. The most common procedures which are described include the #periareola, #buttonhole, #double incision, and #anchor patterns. Personally, I frequently use #liposuction along with the double #incision for larger breasts, and, some variation for smaller breasts; depending upon the position of the areola. The female breast nipple and areola are often centered on the breast. However, the nipple and areola are lower and closer to the outside edge of the #pectoralis muscle in the male patient. Shaping the side of the chest may also be required and can be performed with #suctioning; along with contouring of the muscle, as noted above, to provide the best definition for the chest. Being each person varies, it’s important to be realistic about your goals and what is achievable. Your board-certified plastic surgeon will recommend the type best suited for you. The most important decision to be made before performing any surgical procedure is determining whether you are an ideal #candidate.

If you have excess skin then you will likely require a double incision mastectomy to remove the tissue and give you the best cosmetic results. 

The main reason a larger scar is used is to remove excess skin. As you will appreciate, the larger the breast, the larger the skin envelope. 
As has been suggested, Testosterone may cause some atrophy of your breast tissue, but is slight and it doesn't really help with the skin. Liposuction is another option, but while the breast does have fat, it also has a significant glandular component which is fibrous and resistant to liposuction. Again, it does not address excess skin. The skin can shrink back down, but this is unpredictable and takes time. 
In my experience, I only offer a keyhole type approach in patients with very small breasts, those that are A cups or 100-150grams. 
This surgery really has its best results in patients who are lean with good muscle bulk- because large pecs are what we see in the idealised male chest.  This can also help to hide scars, especially if your surgeon aims to place the scar in the shadow under the pectoral muscle.
It is worth seeking a consultation with a plastic surgeon in your area to discuss your options. Good luck!

This is something that must be determined by your surgeon.  Be sure to chose a board certified plastic surgeon with a great reputation among the transgender community.  

There are several ways to reduce your breast size and this may allow your surgeon to use a keyhole or comma procedure.
1     You can lose weight.
2     You can use testosterone and ttamoxifen.
3     You can have liposuction of your breasts.
I would recommend that you discuss this question with your surgeon.  Your surgeon should have a detailed pre-op check list for you to follow.  Your surgeon is your best resource as he/she is most familiar with your medical history and how you will be healing following surgery.