If you naively consider the topic only from a bodily autonomy perspective, then the answer is deceptively simple: get the blades out and start slicing. But this ignores the wider medical ethics concerns over whether it's the right thing to do for the patient, if the surgeon is causing harm by doing so, if gratifying the patient's short-term desires genuinely helps them in the long-term over their entire life, if it's reasonable to expect a surgeon to perform such a procedure and how they may feel in the aftermath, if there are any other interventions that would be more effective. And societal questions over whether it's ethical to deliberately add new members to a population who already find it difficult to find the support they need, how this will affect others who may now be situational obliged to assist with this person's new disability, and so on.
It makes no sense to focus solely on the individual and ignore the wider context, when there are so many other factors to consider.