/gd/ is pretty cool

fixheader.py

# usage: fixheader.py <valid_bmp> <file_to_fix>

HEADER_SIZE = 54

import sys

header = sys.argv[1]
fileName = sys.argv[2]

with open(header, 'rb') as input, open(fileName, 'rb+') as output:
    data = input.read(HEADER_SIZE)
    output.write(data)