I got curious and had to fire up the ol LLM to find out what the story is about the words that aren't pluralized - TIL about countable and uncountable nouns. I wonder if the guy giving you trouble about your English speaks French.
You can for example have two different organizations with different codes of conduct.
There is though nothing technically wrong with seeing each line of code as an complete individual code and referring to then multiple of them as codes.