Don't you mean, their
old lives?
I'd suppose they'd arrive in the middle of the Dark Heresy era, where there is only war. The New Testament has not been written yet. So given their knowledge of what already happened, they'd be writing bibles with "prophetic knowledge". And once they gain enough cred sets in, Vivio might think that this world can be changed, and start writing the New Testament as she saw fit.
The Word spreads, tides of time change, and the damage to the timeline is repaired. However, we then know the origins of the mysterious New Testament that transformed Ancient Belka from the wartorn apocalypse of dire despair, into the Saint Church.
How perfectly Star Trek.
