No. Assuming you've managed to research, acquire ingredients, prepare, and cast the spell* prior to invoking aspects, it might...though duration needs corrected / clarified. I'm not sure where your duration of 'noon' came from - dusk and dawn are the thresholds.
Changes, when Lea makes a some magical outfits for Susan and Harry, and when Harry makes a snark about hoping they won't disappear at midnight, she responds with something to the effect of "Of course not; what do you take me for, a Summer faerie? They'll last until noon." This implies that Seelie/Unseelie magic lasts until midnight and noon, respectively, rather than until dusk/dawn like most thaumaturgy does.
It's also explicitly stated that you can only buy temporary powers for one scene. (YS92)
Yeah, but I figured you could keep buying the same Temporary powers over and over again each scene. It adds up quick, if you're trying for anything more than a power worth more than one or two Refresh.
*The spell itself isn't going to be easy. You'll need the appropriate symbolic links to start with...good luck getting away from a dragon with anything useable as a symbolic link back to him. Harry went through some fairly extreme measures to get a link back, what do you think the dragon might be willing to do?
The symbolic link is himself; the dragon he turns into is a manifestation/personification of the predatory and possessive instincts that come with the Mantle of the Winter Knight.
EDIT:
Hmmmm. Well, first off, a necklace is only a +1 Item of Power, you'd need a dragonskin cloak or something to be +2,
*checks Item of Power* Hmm, I think you might be right. It's based on whether or not it's concealable, though, not size, so a ring should work. You can't conceal them when you're wearing them openly on your finger, after all. A pin for his suit-collar or tie might also work. Or belts, if he wants to just rip off the Hexenwulf spells.
speaking of which...none of the Tags you list actually explain how he casts the spell. The story of the spell, y'know, what the whole process of making spell declarations is supposed to be about?
Hmm? He sits down, and does a bunch of calculations working out the physical principles of the thing. Then he builds the image in his mind, whips up a circle of ice with Evocation, and pulls on the power of Winter through his Mantle to power the ritual, and the instincts of his mantle to understand how to use his new form, and focuses them through the mental images he has and ties them all off in the item he's using to store the spell.
So no, I wouldn't allow that. Or any spell that was designed that way. On the other hand, getting your hands on the scale of a Dragon (Contacts), finding the proper ritual in an ancient book to assume a tiny fragment of it's glory (Lore), and a single Scholarship Declaration (any one of your three) to understand how to structure it properly, and I might allow it, yeah. Spells must be thematically appropriate in order to work. Indeed, with Thaumaturgy, that and time are their only real limitations, so you damn well better enforce them.
It's not an actual Dragon, so much as the image of a lower-case dragon as a representation of the possessive and predatory aspects of Winter.
I'd also just generally be very skeptical of applying Item of Power or Human Form to any temporary power set. Their disadvantages are mostly long-term, and I'm very skeptical of allowing them on such a temporary thing. But that's a personal thing not the rules. I'd also be very skeptical of any PC grabbing Beast Change on a temporary basis without some sort of possession going on (ala Hexenwulfen, and likely including Demonic Copilot), simply because it's really hard to justify any other way.
Becoming a personification of the worst of the Winter Knight's instincts wouldn't be enough for you?
So, in short, yes, you can do what you're talking about (at the costs in question), but the item needs to be more obvious and you need better thematics for your Thaumaturgy to actually work. And you need an explanation for Beast Change, which you are seriously lacking.
He gets big and strong (increasing Might), and overwhelmed by the instincts of his Mantle (decreasing Scholarship and increasing Fists, Survival, and Stealth), dulling his thought processes. Also, he doesn't have hands anymore, dropping Craftsmanship, Driving, and Weapons to 0.