# -*- coding: utf-8 -*-
import re
text = ur"הmאפrקt boom sam"
result = re.sub(ur'm\b', u'X', text, 0, re.UNICODE).encode("utf8")
print(result)
IyAtKi0gY29kaW5nOiB1dGYtOCAtKi0KaW1wb3J0IHJlCnRleHQgPSB1ciLXlG3XkNekctendCBib29tIHNhbSIKcmVzdWx0ID0gcmUuc3ViKHVyJ21cYicsIHUnWCcsIHRleHQsIDAsIHJlLlVOSUNPREUpLmVuY29kZSgidXRmOCIpCnByaW50KHJlc3VsdCk=