I haven't actually looked at the Religion aims, but if it's a move away from "hardcoded to this fantasy trope" and towards the full 'random' procedural (and slider-for-realism/fantasticism) setting, then it's in keeping with the game's intended direction. For better or worse (it's not just Religion where people might dislike breaking out of the existing bounds - see the fuss over user-suggested Tea for dwarf consumption, before they started talking about energy densities/availabilities in caverns).
It has not been unknown in Roundworld history for a monarch of a land to decree that their subjects shall now adhere to their new (or pre-monarchically existing) thoughts on religious adherence, with various types of trickle-downs from "You must... (and/or" must not") "...now adhere to <insert subtle or otherwise differentiation of faith> now, under pain of Pain" (instead of/on the way to Death) to the rarer "But, hey, whatever floats your boat!", by way of the not uncommon "But the Duchy next door is your kind of place, they'll take you, while we take some of their odds'n'sods off of them".
Inter-'species' conversion? Well, it's not exactly a thing we've seen this side of the Denisovans or Neanderthaals, unless you count the results of the African/etc missionary position, the historic Etheopian Jews (that might have been naturalisation/assimilation), etc. Which I don't.