Do boxers have to register their hands as lethal weapons?

NO ... There is no law in the United States or any common law state that reads that a boxer or for that matter any combat sport ( Karate, MMA, Wrestling ie ...) most register any part of their body as a weapon let alone as a lethal weapons ... There have been court case's were harsher charge for expert in fighting were up held or up grated to reflect the knowledge of the defendants expertise ...