Honestly most of the actual theology of the Imperial Cult is kind of a black box anyway, so I think it's fine to invent your own. In some interpretations of the setting I think it's completely plausible that you might have the Ecclesiarchy equivalent of the Franciscans or even more out-there groups. Especially if it's mostly in the realms of theology aimed at an elite educated audience rather than put into practice.
The only especially interesting source I remember which pointed towards some actual attempt at an actual Imperial moral philosophy RE: aliens beyond simple grimdark aesthetics was from the third edition rulebook. I can't remember the quote exactly, and I'm on my phone, but it was something to the effect that all aliens have human souls, trapped in alien bodies, and therefore the moral thing to do is "free" them.
Obviously that's not particularly better from a "don't commit xenocide" standpoint, possibly even worse, but what I find fascinating is the underlying argument. The author clearly recognises on some basic level that aliens are agents worthy of moral consideration and may share some commonality with humans; it views violence towards them as something needing justification rather than a given. What it makes me think of is a sort of Imperial Thomas Aquinas sitting in a monastic cell somewhere, performing Olympian feats of mental gymnastics to find a "natural law" underpinning and bolstering the Imperium and its actions.
But other than that, I don't recall anything especially interesting or notable on a theological level. So there's a fairly blank slate for making stugff up.
The only especially interesting source I remember which pointed towards some actual attempt at an actual Imperial moral philosophy RE: aliens beyond simple grimdark aesthetics was from the third edition rulebook. I can't remember the quote exactly, and I'm on my phone, but it was something to the effect that all aliens have human souls, trapped in alien bodies, and therefore the moral thing to do is "free" them.
Obviously that's not particularly better from a "don't commit xenocide" standpoint, possibly even worse, but what I find fascinating is the underlying argument. The author clearly recognises on some basic level that aliens are agents worthy of moral consideration and may share some commonality with humans; it views violence towards them as something needing justification rather than a given. What it makes me think of is a sort of Imperial Thomas Aquinas sitting in a monastic cell somewhere, performing Olympian feats of mental gymnastics to find a "natural law" underpinning and bolstering the Imperium and its actions.
But other than that, I don't recall anything especially interesting or notable on a theological level. So there's a fairly blank slate for making stugff up.