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))