Perhaps this could be implemented as a separate mod.

Khorne - Will obviously send raids often, loves slaughter and murder, dislikes psykers and weaklings.
Tzeentch - Likess psykers and research, in extreme cases (you can also add an event for him that randomizes the probability of all events, thereby squaring randomness).
Nurgle - Predictably often makes bad events, even more often infects your pawns with diseases, your pawns will feel pain less.
Slaanesh - Which is connected with the pleasure and mood of the pawns, possibly increasing the effect of both positive and negative thoughts by 2 times.
Emperror of humankind - Likes Astartes, Custodes and Primarchs, dislikes xenos, chaos and unauthorized xenohumans.