I know Gene Roddenberry, NBC, and the Star Trek prop department made several changes to “The City On The Edge of Forever.”
I understand he envisioned an actual city instead of just a talking arch that showed the history of the universe. The city scene was cut, and I’m not sure how important it was to the story.
I also understand he had one of McCoy’s assistants secretly addicted to an illegal drug rather than mcCoy accidentally injecting himself with an overdose.
Even with the edits, it is still one of the best episodes of the series.