Apologies if this has been done to death, but I had a sorta kinda shower thinking revelation the other morning. Some of this is just ramblings, or note taking, and all a bit tin-foily, but the general theory is:

Names are mantles. Mantles are titles - or transferable Names.

Think about names as titles, not as specific names for a moment. Queen Mab, Mother Summer, Uriel. They all have some component of an honorific or a title involved with them (more on that later).

Titles and honorifics are inherently transferable. When a king dies his rights, responsibilities, and powers are transferred to the prince. When a daughter has a child, she becomes a mother, the mother becomes a grandmother. But the nature of that role or mantle doesn't change with tranferance.

We know that mantles are transferable on Halloween. We know that Harry has some mysterious naming power. We know Harry was born on Halloween and was conferred some special power due to this that has all the immortals just a shade on edge about him. I think that there is some aspect of Harry's mysterious power that will allow him to affect mantles through the act of naming - creating new ones, transferring existing ones, and most importantly Harry can change the nature of a mantle through naming whenever he feels like.

I went digging for some more evidence in the wiki:

"A mortal's Name can change over time due to how their perception of themselves can change, whereas most supernatural beings' Name is static and unchanging." http://dresdenfiles.wikia.com/wiki/Name

"A supernatural identity with a mantle may be though of as like a governmental office. Only one person can hold the position at a time, but many people can hold it in succession, and each occupant of the office is delegated the same authority. When a person assumes a mantle of power, the mantle begins to alter its personality of its host. " http://dresdenfiles.wikia.com/wiki/Mantle

These two quotes indicate that mantles aren't meant to change. But Harry was born on Halloween - which is when mantles can change. I would posit he's carried part of the nature of Halloween in his power so that he can personally change mantles.

Thinking of it this way a few other things start to make a lot more sense. One thing that always bugged me about Summer Knight was why on earth would Mab come to Harry to investigate the death of Ronald Reuel? Yes, she likes to act indirectly, and yes Harry knew Chicago, etc etc... but why? Those are good side effects, but not good reasons to force Harry into that book. With this thought, it makes perfect sense. Mab got the guy who could control mantles and Names to go find her lost mantle, or make sure it is changed if it passes to Summer.

When we're in the Valley of the Stone Table then power can flow between Summer and Winter, whereas in most cases a mantle will seek out the closest vessel of the court with which it is associated. Much like a title will only pass from one royalty to another along the lines of inheritance unless there is a war or invasion or some special circumstance that interrupts the laws of inheritance - like the battlefield of the Stone Table.

Harry named the Archive (an inherited mantle) as Ivy and subsequently her nature changed some - to her detriment, but giving her a name changed that mantle.

Uriel was angry when Harry altered his name because he knew it could change his nature. "Uriel said that the "el" part of his name an important part of who and what he is."

Toot toot has essentially gained a minor mantle as Major General of the Za Lord's Guard. Interestingly, harry named himself the Za Lord in a way and as such has a desmense in fairie. I think we'll see Toot-toot reveal the Za Lord's lands in Fairie at some point.

Edit: He Named Lash and changed her nature from Lasciel.

"Bob" wasn't always Bob - he became Bob when Harry gave him a Name.

That's all I have right now, but I bet ya'll have some thoughts. I think this may prompt my first re-read in a while with a focus on Harry's control of various mantles through Names.

edit: more examples.