“Unusual”, being uncommon or outside societal norms, is a poor framework for denying treatment. Only a few decades ago, transgender people wanting to undergo cosmetic plastic surgery was deemed “unusual” (in many places, it still is), yet today we generally consider it one of many appropriate treatments for gender dysphoria. There isn't an ethical principle saying things can't be “unusual”, this is actually a logical fallacy: argumentum ad populum. If the only thing stopping someone from getting some sort of cosmetic plastic surgery is that it is “unusual”, they should be able to get the surgery.

At the same time, we cannot pretend that there aren't usually mental health issues at play when someone wants to permanently change their appearance in an unconventional way. The patient should have to get psychological treatment first — if the practitioner deems mental health resources to be insufficient and OKs surgery, then cosmetic plastic surgery can go forward.

This is all assuming that the surgery does not harm the patient. If not, then the question “Does someone have the right to knowingly harm themselves?” comes into play. To that, I would lean on the side of no.