code: def tamper_file_at(path, pos=0, replace_str=None):
      
      if not replace_str:
          replace_str = "\x00"
      try:
          with open(path, "r+b") as fh:
              if pos < 0: # if negative, we calculate the position backward from the end of file
                  fsize = os.fstat(fh.fileno()).st_size
                  pos = fsize + pos
              fh.seek(pos)
              fh.write(replace_str)
      except IOError:
          return False
      finally:
          try:
              fh.close()
          except Exception:
              pass
      return True
docs: Tamper a file at the given position and using the given string