Did I say there's no room for deviation? No. Did I say Blizzard doesn't really deviate from it? Yes. I know I lack in my understanding of English and for example I still don't see how Cenarius is actually either a Dwarf or a human, but these sound different to me. But who knows, I could be wrong. And Darkfallen aren't mutated with exception of females. They only have a darker skin tone. Which by your criteria from previous post, does not make them a different species. Especially since undeath itself doesn't really fit them one way or another. Why would it alter your species anyway? Does it begin with the corpse, or resurrection? If it's the latter, does non-undeath resurrection count? Does being brought back by doctors? At best they'd be a race. Which is the only deviation by Blizzard that I can think of in terms of lore (in terms of gameplay Worgen are called a race in character creation), since Forsaken are called a race by Sylvanas. No other undead are though, at least if I recall correctly.
So race with an Ŗ? Or was it small ŗ? Then again Scythe of Elune has a fiery skin so it has a sort of a diurial aspect to it while undeath sounds entirely nocturnal to me, so maybe Worgen are a race with an Ř/ř? And then there's the Mechagnomes which have normal "r" but the "c" is silent.