My main contention is in characterizing Mab as (knowing/willing) part of that alliance. Correct me if Im wrong, but the only evidence you site that she is working with them is that bit from bob in GS. But Bob's theory that they were working together was purely based on the fact that there was an unusually long winter indicating that she was still in town.
I don't have the text to hand, being in work right now; are you sure of that ? I thought that conversation came just after Harry mentioning that he'd had a long conversation with Bob that isn't in the text verbatim, implicitly about events we've already seen, and that the point I made in the original post about Uriel's reaction to being summoned and how that pushes Harry towards choosing to summon Mab could well be relevant there. I'm not recalling that the excessive winter confirming mab is around in Chicago was in that conversation at all, though I could well be wrong/
Which we later learned was because Uriel had, apparently against her wishes, taken Harry's soul on walkabout, forcing her to sit still on earth and give mouth-to-mouth to a human for months, out of season and at great personal strain. All so he could teach her new pet that he she was mistaken in her belief that she could mold him at her whim. And in this case at least we can be certain that she was not simply misleading him as part of some greater manipulation, since we have a WOJ that she was being entirely Truthful, and just happened to be entirely Wrong. If it were all a collaborative scheme between her and Uriel, that could not have been the case.
The "apparently against her wishes" there strikes me as rather clever.
Mab says she's cross with Uriel for sending Harry's soul walkabout. She also says that had Harry not made it through that he'd have been lost and gone forever. She puts those two sentences right next to each other and leaves Harry and us to infer a causal linkage. However, the grammatical form "had Harry died as a wandering soul, he'd have been gone forever" (I paraphrase from memory) is the same as "had I a billion dollars free and clear of obligation, I know exactly which good causes would receive the first $800 million of it"; it can be (and in my case is) perfectly true without requiring me to actually have a billion dollars, or for it to be a remotely plausible eventuality that I might have any time soon.
I think "She cannot change who you are" makes sense because Mab and Uriel see the universe in very very different ways. Mab cares about results. Uriel cares about choices. Mab's is an ethic of consequence, Uriel's one of free will. I'm not seeing that the ways the Winter mantle may change Harry matter a bent penny to Mab
except to the extent that they make Harry more likely to do what she asks of him without qualm.
We have the evidence of SmF that Mab can seriously change the range of options Harry is aware of, and in so doing, guide the choices he makes toward a desired end. This does not seem to count as a violation of free will, at least at the scale at which Uriel cares about and is allowed/required to oppose such violations. We know from BR (and I can never remember whether this is Harry having breakfast with Kincaid and Murphy, or the screen with Harry and Bob immediately before; it's the conversation about Renfields) that it is possible for humans to be enthralled with such a fine touch that they do not even notice. Harry does not notice Mab messing with his memory in SmF; it takes Molly looking through his mind to find it, it takes Michael being suspicious that Harry has not lost Lasciel's shadow after all to motivate that search, and even when the mental block is found, Harry actively cannot resist or overcome it by will alone; that takes Michael's prayer, which looks to me like direct divine intervention.
The take-home message at the end of the day would appear to be: Mab can't change what Harry is in the sense Uriel cares about. But apart from that, she has pretty much free rein to manipulate what he
does, which is what she cares about.
And what that achieves, that benefits all participants of Team UMO, is a Winter Knight who is willing to go along with being Winter Knight for the moment, rather than engaging in elaborate suicide attempts, because he is under the impression that Mab not being able to change who he is means he can meaningfully resist her wanting him to do something he finds objectionable. Harry saying "I will go along with this for the moment and make trouble if i see a need for it" is much more productive than Harry saying "I'm not doing any of this under any circumstances because it makes me a monster", and I think we have plenty of evidence for Mab's ability to convince Harry to do what she wants in any specific case where that's important (as seen in SK and SmF.)