My residency program doesn't do a ton of cosmetic training, maybe a week or so each year of you actually doing it yourself. Would this greatly hamper your ability to find a private practice job? I'm not terribly interested in cosmetics, but I do want to be marketable, and I know most private practices offer cosmetics. Is this something that can easily be picked up / improved on after residency? My understanding is that cosmetic training is minimal at many residency programs, so I don't imagine this is a unique problem.
I wouldn't worry too much. I think, contrary to popular misconception, most general dermatologists mainly practice....general dermatology. The cosmetic market is competitive and there is more limited "patient supply". While there are some dermatologists/plastic surgeons/ENTs, etc. who concentrate exclusively on that, most dermatologists do it as a "side-gig" (e.g. 10% of patients or less). There are also opportunities to get training on this after residency - either CME conferences, AAD Meetings, weekend courses, cosmetic fellowships, etc. You should also consider choosing a private practice where you feel other providers would be willing to teach you if you ask for it. For lasers, you can also always have a company rep come out to your clinic to teach you and practice on volunteer patients and/or nurses/MA. They want you to use their laser.
I personally recommend in your first year as an attending, especially if you haven't done a lot of cosmetics, to (1) not to do any cosmetics in the beginning (2) once you're adjusted to your work schedule, flow, patient-ramp up, have all your note templates, etc. and clinic is going well...then consider slowly adding in cosmetics - maybe start with botox first (easiest), then filler, then an easier laser like PDL. (3) Branch off to more advanced stuff (e.g. ablative / resurfacing lasers, tattoo lasers, etc.) if you feel so inclined.
Personally, I find cosmetic patients exhausting, and anything beyond the occasional PDL case and/or neuromodulator patient is more than I want to do. I also have seen enough patients with terrible filler complications from other providers, and know I don't have the personal will or desire to do enough of it in my practice to feel comfortable with the adequacy of volumes to maintain skills....that I don't do filler nor really want to. I actually got a lot of cosmetics training in residency (not sure about these comments about issues with product - Galderm/Allergan love donating botox/filler for residents to practice so they use their product once they're attendings). I'm sure other dermatologists will have a different perspective.