Ooooh, that's a great question! I just automatically assumed that they can simply because they're not ~actual ghosts~, but it doesn't have to mean that at all, so it's entirely possible that they cannot.

It seems quite possible to me that it's an unknown, in that none of the others ever try to do meritous deeds, you know? They probably assume they can't register them, because of All The Darkness, but maybe that's just an assumption.

Then Shen Wei would be able to do it because of Kunlun who made him part-god, yes!

This also seems entirely possible! *is completely agnostic about the cosmology* ;-)

That's kinda exactly how the novel backstory works for me, lol - even when I remember what happened, I keep forgetting which parts actually happened in-world, even after I already figured some of them out. xD

Yeah, I remember handwaving vast swathes of volume 3, lol. :D