It's changed drastically since release. There are lots of people out there who have noticed this and many have saved examples of before and after responses to prompts.
The "content moderation system" is new, so I don't think it changed. What, however, changed during the time ChatGPT is live, is what kind of prompts it refuses to answer, because the topic is offensive/inappropriate. It had hilarious versions where it would tell you a joke about men about not about women or one ethnicity but not the other.