http://www.imperial-library.info/content/changed-ones states that: "[Boethiah] demonstrated the right way to wear their skin." - I find it odd that Azura isn't even mentioned in this account. This book is also a quote from Skeleton Man's interview which I'm not sure whether or not that interview took place before or after Morrowind's release - which might lead me to question its full weight in consideration of the truth. But it DID end up being a book in the final game.

Goodall confirms this view in one of his posts: "Only Boethiah can change a race's skin. Only the Dwarves can cover it in tin foil."

http://www.imperial-library.info/content/battle-red-mountain seems to pin the deed on Azura: "And then, in that moment [after Azura curses the Tribunal], all Chimer were changed into Dunmer, and our skins turned ashen and our eyes into fire. Of course, we only knew at that time that this had happened to us, but Azura said, 'This is not my act, but your act...'"

http://www.imperial-library.info/content/nerevar-red-mountain also says that Azura took the cookie from the cookie jar: "And so that they might know forever their wicked deeds Azura changed the Chimer into Dunmer, and their skin turned ashen and their eyes into fire."

The two former accounts have their reliability questioned even in the game itself, due to the fact that they come from a biased source.

http://www.imperial-library.info/content/sotha-sils-last-words (not quite official) also blames the deed on Azura: "Azura punished them, and their peoples (yes, including me!). The dark skin and fiery eyes is a visible and alarming reminder. Is this coincidence that the change happened upon the breaking of the oath? Azura is indeed the culprit. Had the "Tribunal" not undergone this deed, Azura would have taken no action."

Is it given knowledge that Azura cursed the Chimer and transformed them into the Dunmer? Or is there controversy over this? Is this just something that was changed from the original design, like so many other things and as such the "Boethiah did it" stance is outdated?

It might just be me, but in most accounts of this event (including the ones I've listed here), Azura seems to skirt around actually claiming responsibility for the action beyond simply issuing a curse and a promise. But the act appears like it could have been orchestrated by Boethiah. However, we have the information from the Khajiiti origin myths that Azura DOES have power to alter races.

So is there a definitive response to this?

The book "The changed ones" seems to refer to the origin of the Orsimer, instead of the Chimer > Dunmer transformation.

I don't think that's accurate. It clearly says that he taught the "Changed Ones" (the meaning of Chimer) how to "...build Houses (with a capital "H"), and what items they needed to bury in the Corners. He demonstrated the right way to wear their skin. He performed the way to walk to achieve an Exodus." - to me this obviously refers to the Chimer.

Also Skeleton Man's interview, which this book is derived from, is referring to the Chimer. Not the Orcs.

I don't have any basis for this, but I tend to believe that the transmogrification of the entire race was more a direct result of tampering with the Heart. A vaguely similar event to the disappearance of the Dwemer - but much less impressive. Possibly the Tribunal were even right in claiming that it was a blessing - the dwarves were truly cursed, because they knew the right things to wish for. Azura saw this before the Tribunal and seized the opportunity to convince them of her power. A pretty weak explanation, since I doubt that Sotha Sil himself would be convinced by this. Boethiah is involved, because in some way, the apotheosis of the Triune revokes Boethiah's blessing on their people.

The Changed Ones is talking about the transition of a proto-altmeri people into the Chimer, not the Chimer into the Dunmer. Those are two very different events.

I'm inclined to an interpretation such as this as well. Azura's a conniving one. And in one of these accounts she admits that it will take her a long time to gather the power to resurrect on individual (Nerevar). And the new Tribunal laugh in her face when she curses them; Sotha Sil certainly seeming unbelieving.

You are right, thanks for that observation. But was there a skin change from "proto-altmeri" to Chimer then?

Currently, it's believed that the Chimer would have looked like their bretheren on the Summerset Isles. I think "right way to wear their skin" is best interpreted as a metaphor, perhaps for a sentiment such as "right way to carry oneself."

Hmmm. It could be simply metaphor. I forget, in the timeline, did this event (proto-altmeri to chimer) take place when races are described as having difficulty holding shape? Back in the merethic era? Azura would have stabilized the Khajiit at this time.

Or I could be completely off basis with this ludicrous claim on lore, but I thought I remembered this being a thing...

edit: I think this is where I got this idea from originally "And Nirni stopped weeping, and Azurah spoke the First Secret to the Moons and they parted and let Azurah pass. And Azurah took the forest people who were torn between man and beast, and she placed them in the best desserts and forests on Nirni." - http://www.imperial-library.info/content/morrowind-words-clan-mother-ahnissi-her-favored-daughter
Though, for whatever reason I applied this identity crisis to all the races at the time.