Is reducing a protruding occipital bone (with bone bossing) by several millimeters considered a safe procedure? (Photo)

As with any cranial (skull) deformity, it is possible to do some correction without doing complex craniofacial procedure. In your case, I do not see much of a reason for protrusion to be corrected; it looks quite normal to me? In the case that you insist on reduction, it is possible to achieve minor change shape by "shaving) tuberosity and some occipital prominence with a bur. An experienced, board certified plastic surgeon with background in craniofacial surgery, would be a good starting point. Good luck.

Occipital skull reduction is a safe procedure as it only removes the outer table of skull bone. The question in occipital skull reduction is not whether it is safe but whether given the amount of bone that can be removed if that will make enough difference in the back of head protrusion to satisfy the patient.