Yeah, I'm not expecting it'd be feasible to write alternate endings without the mind control stuff (I was pretty impressed by the non-futa rewrite of the Satyr ending - I'd expected just going into the sheep ending), since it seems like a pretty integral part of the corruption theme you're going for. If you're gonna have an SFW mode, going into that for select scenes seems more reasonable.
I think the cheapest way to let players avoid stuff that'd make them uncomfortable would be some sort of tag-based content warning system? Give scenes some tags describing what's in them and give Qades a list of the tags that the player can put on a watchlist. If an upcoming scene is tagged with something the player's asked to be warned about, have a pop-up appear at the beginning prompting the player to skip it using the existing skip ahead function, or maybe automatically switch to the SFW version of scenes that have one.
Idk, I'm just spitballing.