code: def write_trailer(self, sector, key_a=(0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF), auth_bits=(0xFF, 0x07, 0x80), 
                        user_data=0x69, key_b=(0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF)):
          
          addr = self.block_addr(sector, 3)
          return self.rewrite(addr, key_a[:6] + auth_bits[:3] + (user_data, ) + key_b[:6])
docs: Writes sector trailer of specified sector. Tag and auth must be set - does auth.
          If value is None, value of byte is kept.
          Returns error state.