Can someone get cranioplasty for cosmetic reasons?

Yes. Usually cranioplasty refers to opening of the skull to deal with brain tumors, bleeding or aneuryms but the root words, "cranio" can simply mean anything related to the skull and "plasty" can refer to shaping surgery. Some people have abnormally shaped skulls. Such surgery may be solely cosmetic to change the shape, for functional reasons to relieve pressure on the brain or sometimes a combo.