import re
strs = ['1234 foo foo', '19 bar bar', '0 baz baz']
rx = re.compile(r'^(?:(\d{1,2})|(\d+)\d{2})(?!\d)')
for s in strs:
print(rx.sub(lambda x: '100' if x.group(1) else x.group(2)+"00", s))
aW1wb3J0IHJlCnN0cnMgPSBbJzEyMzQgZm9vIGZvbycsICcxOSBiYXIgYmFyJywgJzAgYmF6IGJheiddCnJ4ID0gcmUuY29tcGlsZShyJ14oPzooXGR7MSwyfSl8KFxkKylcZHsyfSkoPyFcZCknKQpmb3IgcyBpbiBzdHJzOgoJcHJpbnQocnguc3ViKGxhbWJkYSB4OiAnMTAwJyBpZiB4Lmdyb3VwKDEpIGVsc2UgeC5ncm91cCgyKSsiMDAiLCBzKSk=