Kieran part was joke
Changing dwarf into human. I you sure it's impossible. You just need demon and a lot of blood he will tell you when to stop bleeding. Mythal is elf who is human so.
I highly, highly, highly doubt that blood magic can do that. It is powerful, yes, but that doesn't mean it can do anything.
We don't really know what Mythal was. She could've been a spirit, a powerful elven mage, or something else. She joined to Flemeth in a similar way to how Justice joined to Anders. Did that make Justice a human? No, he was still a spirit, but he was bound to Anders.
Cory not a "real" darkspawn. (He pretty much Emissary with his own mind) He is first ghoul, he not born darkspawn he born normal human and was infected by blight. Blight is disease where is not separate human/elfs/qunari.... and darkspawns, we have hurlocks human darkspawn, shriek elfs... Darkspawn are "humans" who born already infected. And how many fully transformed ghouls we saw? Maybe ghouls eventually become "real" darkspawn, probably not.
And yet he is one of the very first darkspawn, and emissaries are still darkspawn. Yes, he was born human, but he and the other magisters were changed into darkspawn when they entered the Black City. All we really know about the Black City is what is stated in Chantry lore and what Cory himself said, but even then, there's no guarantee any of it is 100% accurate.
As for the darkspawn, they are born as they are via broodmothers, which originate as female humans, dwarves, elves, or qunari. Broodmothers are formed in the span of a couple weeks, while ghouls stay ghouls for years until the corruption consumes them, or they die in combat (raid, Blight, etc.). Darkspawn don't age and are essentially the taint made manifest, so the only way they die is in combat. The various races of Thedas have limited lifespans, though the elves originally had very lengthy lifespans comparable to the asari in ME, so there's basically no real comparison between darkspawn and the races of Thedas beyond height (excluding ogres). Darkspawn are darkspawn. There's no changing that. Unless we get some Mary Sue/Gary Stu character that goes around curing the taint and making darkspawn into people.
You say. It's a physical corruption, This I agree. Blight is just disease, and disease can be cured flesh can be easy moulded. We have shapshifters Flemeth/Morrigan. Qunari are probably elfs who was changed using dragon blood. So curing blight is not impossible, but seeing Bioware record, we will find cure so easy, with most stupidest way possible,I hope I am wrong.
Not entirely sure what shapeshifters have to do with this, tbh. Still, Flemeth seemed to be immune to the taint (remember how she killed all those darkspawn in DA2 in her dragon form?), which could be for a number of reasons given what we know about her. Morrigan, on the other hand, we don't really know.
Qunari being elves at one point is simply a theory which will likely be debunked some time in the future (imo). That's a very poor example.
I wasn't disagreeing about the possibility to cure the taint. I was disagreeing about you saying that the darkspawn could be made human. Even if it was possible, considering what happened with the awakened darkspawn in Awakening, do you really want to risk 'curing' them and potentially letting a hoard of homicidal and mentally unstable people run around Thedas? Plus, how would Thedas survive with the sudden and massive influx of people? Resources would be depleted incredibly fast and soon enough, there wouldn't be room for anyone.
While it may seem like a good thing to 'cure' the darkspawn, it can cause immense damage to Thedas as a whole. Especially in the long run.