My most recently published story ("The Collector" in Dead Souls) takes place on a post-battle battlefield - Byzantine Empire troops vs Slavic villagers. It would have taken place somewhere around 600-800 AD. Or is that CE? Regardless... At that time, the Byzantine Empire is a solidly Christian entity, the Eastern Roman Empire, after Rome itself has fallen, and before the Schism that divides the Church in name as well as in fact. The Slavic nations are not at that point Christianized.
In my story, there was some mention of religion, but I'd mostly envisioned this as territorial Empire expansion. That religion follows is ... expected. But that wasn't really the point of the story.
The book went through some difficulties. For reasons unknown, the original editor and the publisher parted ways, and the publisher took on editing duties.
The main characters of the story are a Slavic villager, the young Byzantine soldier who killed the villager's son, and a crow. The original editor sent me back edits that included two critical word substitutions. In both cases, he substituted "Byzantine" with "Christian." Just two words, out of 2500. That was all it took to dramatically change the meaning of the story. The story was now about forced Christianization. Bad Christians vs Good Pagans.
Not my intent at all. Whatever my own thoughts on the subject, I had not intended this story as an anti-Christian screed. But it seemed that a heightened level of religious commentary was in the cards. So I ended up adding a bit that universalized the bashing - the crow, as POV character, reflecting that as the various players suffered, none of their gods showed up to help them.
Later, when the editors changed, I was able to strip most of this stuff back out and bring the story back to what it was meant to be.
Still, an eye-opening experience, and that will stick with me. You can't substitute cayenne for cumin and expect to get the same dish.