Once you're medically licensed you can kind of do whatever you want, so long as you can find an institution to credential you and insurance providers who will reimburse you for your work. Non-dermatologists do nevi resections, botox injections, etc all the time. You can go the cash route, but understand that the people willing to pay cash for cosmetic services generally care who is doing the procedure and may not want to pony up the $$$ for a non-dermatologist, but even then there are still avenues to make money.
With that said, medicolegally, you will be held to the Standard of Care should you ever end up in court - meaning if you fxck up you will be held to the standard of someone board certified in Dermatology. Just as how it's not usually a great idea for non-surgeons to do appendectomies or craniotomies, it's generally not the greatest idea for non-derm people to be prescribing biologics, steroids and doing Mohs surgeries.