On the subject of Mab lying and Uriel confirming it:

Mab is not lying, Uriel is.

Harry confirms that Mab is absolutely capable of changing him. He just makes her realize that doing so is not without consequences, that the very wiles and guilefullness that leads him to defy her are the very qualities that makes her want him as her Knight in the first place.

Uriel is lying when he says Mab can't change him, and Harry knows he's lying. But the truth of his seven words is irellevant. They are encouraging, and they let Harry realize he can still fight becominng a monster, even beholden to Mab.

Uriel has to balance the scales against the shadow' lie. The shadows lie clouded Harry's ability to choose to keewp fighting, to never give up. Uriel's lie let Harry see that there were options. (IE that even though Mab definately could change him, he also could definately convince her not to.)

I think you make an excellent point here, but I actually don't think either of them is lying.

Mab says she can "shape him as [she] please[s ]," but from her perspective, this means that she can get him to do what she wants. Which she can.

Harry's contention is that this is true, but based on Uriel's whisper that Mab cannot change him, and Uriel's earlier insistence that Harry "is a soul, [but has ] a body," she can ONLY change his behavior, not his soul.

Now, certainly, when a human being is told by an authority figure to do something, they will usually do it, even if it seems extreme (see: Milgram's experiments), and a human being placed in a role will often come to embrace that role and the traits stereotypically associated with it (see: the Zimbardo or Stanford Prison Experiment), and that people can derive their beliefs and attitudes based on perceptions of their own behavior (see: Bem's self-perception theory) . It is not, however, a guarantee. Mab admits that what serves her "purpose" is a free-thinking individual mortal to carry out her dictates. Harry's response, based on his understanding of Uriel's whisper, is that he will carry out her instructions to the letter, but go no further, take no initiative, and never, ever do things that she wants him to do on his own, using his own free will. He will never choose to commit these acts. And that is how Harry subverts her plan for him: he simply uses the threat of never making another choice to rob her of the champion she wants.

Of course, she's probably running a long game that in Book 16 or 17 will come back and bite Harry in the ass. I've learned a few things over the past 13 or so books.