I did a aesthetic/breast fellowship with Pat Maxwell almost 20 years ago. I enjoyed it, but I don't know that it's that valuable for most people who've done a lot more of breast and post bariatric stuff during residency.
Honestly, you really learn how to do cosmetic cases from your experience doing recon cases (breast cancer recon, breast reductions, facial fractures, hernias, panniculectomies etc....). Those are the fundamentals vocabulary for most cosmetic cases where you learn how to do stuff.
You don't want to learn cosmetic surgery on cosmetic patients as you can "break a lot of eggs" with the learning curve.