crc_patch.py

#!/usr/bin/env python3
import sys
import crc16

crc = 0

data = open(sys.argv[1], 'rb').read()
crc = crc16.crc16xmodem(data)
print(crc)

padded = data + bytes([crc >> 8, crc & 0xFF])

crc = 0
crc = crc16.crc16xmodem(padded)
print(crc)

open(sys.argv[1], 'wb').write(padded)