Here's a version of Summer Knight!Harry post-Changes where he got the mantle after Summer Knight. I figure the broad strokes mostly wouldn't change until Ghost Story: he'd still end up with Lasciel's shadow, he'd still find out that Thomas was his brother and help make Lara the power behind the throne, he'd still end up involved in Dead Beat (and still have to start working with Lasciel's shadow because Summer would be no help with necromancy), he'd still rescue Molly, still get involved in White Night), still end up rescuing Marcone and Ivy, Morgan would still come to him in Turn Coat, he'd still wipe out the Red Court in Changes.
Major differences would be:
-he wouldn't get made a warden in Dead Beat, and so would get involved with the war as Summer's representative (because the Red Court invades faerie territory in that book)
-as such, he wouldn't be training baby wardens, and would instead spend that time fighting on the front lines
-he would be able to react faster at the end of White Night, so he would still have access to the redeemed Lash
-the roles of Summer and Winter would be reversed in Small Favor, and it would be Summer raising a fuss about the Accords violation rather than the White Council
-as such, he still owes Mab two favors, and that's a lot bigger problem than it was in the books
-he'd do better against the skinwalker in Turn Coat, and Listens-to-Wind might or might not have had to step in
-Morgan would survive Turn Coat (Summer would help Harry with healing)
-he wouldn't kill himself after Changes
That's the point where things would go totally AU, so I'm not going to try to stat it out.
High Concept: A Dark and Stormy Knight
Trouble: Titania Hates My Guts
Other Aspects: Brothers and Sisters in Arms, I Hold With Those Who Favor Fire, Passion is Power, Protector of the Innocent, Stubborn as Hell
Skills:
Fantastic: Conviction, Discipline, Lore
Superb: Athletics, Intimidation, Presence
Great: Endurance, Alertness, Weapons
Good: Investigation, Deceit, Performance
Fair: Guns, Rapport, Empathy, Craftsmanship
Average: Might, Fists, Survival, Burglary
Stunts:
Arcane Lore (lore)
Infuriate (intimidation)
Too Fast to Hit (athletics)
You Don't Want Any of This (intimidation)
Powers:
Listening [-1]
The Sight [-1]
Soulgaze [-0]
Wizard's Constitution [-0]
Evocation [-3]
Thaumaturgy [-3]
Sponsored Magic (Summer; stackable) [-3]
Sponsored Magic (Demonreach) [-1]
Sponsored Magic (Soulfire) [-3]
Inhuman Mental Toughness [-2]
The Catch (threats to those he loves) [+0]
Refinement [-6]
Marked by Power [-1]
Magic:
Evocation (fire, earth, air, spirit, summer): +2 fire control, +1 summer control, +2 fire power, +1 air power
Thaumaturgy: +1 divination complexity, +1 biomancy complexity, +2 crafting frequency, +2 crafting control
I switched his spirit refinement for air because I thought it was more thematically suited, and I didn't give him strength/speed/recovery powers because per Paranet Papers I'm pretty sure he gets that from sponsored magic.
He also almost certainly has a bunch of refinements for item slots, and a bunch of really cool items, since per WoJ making items is one of his specialties and summer likes to give its Knights weapons rather than doing the Winter thing and treating them like weapons--I figure the Summer equivalent of Mab's "I'll try to kill you every day with no equipment" thing would be giving Harry a workshop full of magic supplies and some weapons training. (What kind of new equipment do you think that he would have?)