Can confirm, turning NTR off initially allows you to turn it on later and view the bad endings. I never knew the optional NTR resulted in bad endings and alternate scenes, had quite a lot to look at again once I read about thatThere is NTR in the main game. I forgot if it was ever changed, but there was a time if you started with NTR off or borrowed a save with NTR off, you could no longer turn NTR on or view it.
I only ever played with NTR on so i don't know if that was ever changed.