If I were to pierce my navel would I go to hell?
If you go to hell, I doubt that body piercing will have much, if anything to do with it. I know many Christians who have piercings, although usually it is the ear, for either men or women. I don't know how many Christian women I know who have pierced navels, because most of them dress modestly enough that I would never know. I know of no specific passage in the Bible that says body piercing is a sin.
Even if it were a sin, I don't think you would go to hell specifically for having a pierced navel. People will go to hell because they are sinners. Since all people sin in many ways, all would go to hell, if there weren't a savior to take away that sin. That is the point of the Bible; that man sins and that God has provided a way of escape. Christians believe that way of escape is only through the son of God, Jesus the Messiah, who was the only person to live a sinless life (Hebrews 4:15) and took upon himself all the sins of the world. "Therefore as by the offence of one judgment came upon all men to condemnation; even so by the righteousness of one the free gift came upon all men unto justification of life. For as by one man's disobedience many were made sinners, so by the obedience of one shall many be made righteous." (Romans 5:18-19)
Basically, then, all will go to hell, unless they follow Christ through faith, turning away from trying to sin, immersion in water, and continuing to walk in his way. Even if piercings were a sin, which I am not convinced they are, people would probably go to hell based on more than that one sin. Likewise, if one is saved by the blood of Christ, one sin, if one is sorry for it, will not condemn them to an eternity in hell.