What is body modification? According to the definition employed by “Modify” directors Jason Gary and Greg Jacobson, it’s liposuction, body-building, plastic surgery, tattooing, piercings, sexual redesignation and suspension — the hanging of one’s body on hooks. “Once you’ve done this,” says one suspender, “the rest of your life is a piece of cake.” A plastic surgeon suggests that even shaving, or combing your hair, is a manipulation of your body and therefore eligible for the category. Such a wide definition allows “Modify” to make parallels between the most benign and the most radical transformations. The film delves into the practices and philosophies of those who augment their bodies, be it for vanity or artistic vision.