Append some string in place after a multiline match

append.py

#!/usr/bin/env python

import re, sys

filename = sys.argv[1]
match = sys.argv[2]
append = sys.argv[3]

f = open(filename, 'r+')
content = f.read()
new = re.sub('(%s)' % match, r'\1\n%s' % append, content, 0, re.MULTILINE)
f.write(new)
f.close()

invocation

$ ./append.py /path/to/file '^find these\ntwo lines$' 'and append\ntwo more'