As a resident, it falls under supervision of your attending. Once you graduate you can then start with the cosmetics in your own practice. I don't know if there are any restrictions about obtaining botox or filler for BE vs BC but I doubt it.
OB/Gyns and dentists even do Botox. No certification required. It just falls under license and whether the person doing it is ok with dealing with risks of a bad outcome/litigation. I'm not a cosmetics expert, but for example a Derm 10 years out doing botox with a bad outcome on a patient vs a Dentist doing it for 2 months with the same bad outcome could have different outcomes in court if it came to that.