import re
texts = [' 12345 = "Section 3 is ready for review"', ' 24680 = "Bob to review Chapter 4"']
add = 'Complete: '
key_words_list = ['Section', 'Page', 'Heading']
pattern = re.compile(fr'^\s{{2}}[0-9]+\s=\s"(?!(?:{"|".join(key_words_list)})\b)')
for text in texts:
print(pattern.sub(fr'\g<0>{add}', text))
aW1wb3J0IHJlCnRleHRzID0gWycgIDEyMzQ1ID0gIlNlY3Rpb24gMyBpcyByZWFkeSBmb3IgcmV2aWV3IicsICcgIDI0NjgwID0gIkJvYiB0byByZXZpZXcgQ2hhcHRlciA0IiddCmFkZCA9ICdDb21wbGV0ZTogJwprZXlfd29yZHNfbGlzdCA9IFsnU2VjdGlvbicsICdQYWdlJywgJ0hlYWRpbmcnXQpwYXR0ZXJuID0gcmUuY29tcGlsZShmcideXHN7ezJ9fVswLTldK1xzPVxzIig/ISg/OnsifCIuam9pbihrZXlfd29yZHNfbGlzdCl9KVxiKScpCmZvciB0ZXh0IGluIHRleHRzOgoJcHJpbnQocGF0dGVybi5zdWIoZnInXGc8MD57YWRkfScsIHRleHQpKQ==