Will masturbating after open inguinal hernia surgery damage my repair?

Hard to know: What someone does during self sex will very from person to person. Since we have no information on your pre-surgical health, the difficulty of your surgery or your level of recovery, it is not reasonable to assume there is a blanket answer. It would be more reasonable for you to call the surgeon & ask when you can resume sexual activity. You don't need to mention what kind.