If you're asking if it's canon and consistent of what we know of White Court Vampires in the Dresdenverse, no.

If you're asking whether your GM could allow you to do it, sure, why not ... a GM can theoretically allow you to be part man, part aircraft carrier if he or she so chooses.

Some of you may disagree with me, but I'm pretty damn certain that the 'demon' part of being a WCV isn't actually literal as it is a personification of the Hunger. There's no Demonic Co-Pilot attached to the WCV template and even Harry's use of the sight is highly laden in imagery and metaphor. The one thing we do know for certain is that White Court Vampires are born that way and either turn in their teens when they give it to their hunger, or find True Love/Hope/Courage/whatever and become human. There hasn't been a single example in the books of WCV that did not inherit it from birth.

This is how I would do a cursed Blade

Kilkash [-3]
Description: This sword was passed down through the lines of the Byzantium Kings and contains a powerful curse, those who wield it will crave more and more power until they are eventually destroyed from the inside.  

One Time Discount: A full Arcadian Scimitar is sight to behold and one that is very conspicuous and grants a +2 refresh discount.

It Is What It Is: Kilkash is an Arcadian Scimitar and as such is a large slightly curved blade with a handle set with black onyx, weapons 3

Unbreakable: It is said if a true and noble king was to ever wield the sword its cursed would be lifted.

Imparted Abilities:

Feeding Dependency Power [+1]: The Blade imparts great power unto the wielder at a cost as it comes with all the hubris of Gilgamesh and unquenchable thirst for power which if not satisfied will devour the user of the sword. (anything which is either raising yourself or lowering someone else qualifies as helping your hunger).
  
Supernatural Speed [-4]
Supernatural Strength [-4]
Inhuman Toughness -1 [catch + 2 Women]
Inhuman Regeneration -1
Incite Awe [range] -2

Refresh -9

Bitter, just a quick note ... a catch cannot reduce the refresh cost of Toughness powers below -1. So since you have -2 in Toughness powers, the catch would be a +1. Otherwise, it's a mighty fine blade

I figured it was possible to do a grapple with an evocation block, and the Orbius spell on YS294 confirmed it.

A regular block involves the attacker actively spending his actions each turn to keep his target grappled. But it doesn't say so on the Orbius spell.

Would you rule that a wizard needs to actively concentrate on his target to maintain the grapple, or do you feel the extra shifts spend for duration on the spell covers it and allows the wizard to do some other actions on his following turns? On one end, it seems overpowered that a wizard can completely incapacitate a target for several rounds while acting. On the other end, the amount of shifts put into this long term grapple, especially given the chance he victim can break free anytime, could cost you a great deal of mental stress.

Also, could you duplicate a similarly incapacitating, but maybe not damaging, version of this with a maneuver evocation instead with an Invoke for Effect? After all, someone also needs to roll each turn to break free of the effects of a maneuver's aspect.

Yup, I'd say the rules covering Beast Change and human form fit here since there's absolutely gotta be some skill rearranging between the Adam form and He-Man. The difference between the two is pretty noticeable.

Don't forget to build Castle Greyskull with some really sick Ward and Threshold! I used to have a huge childhood crush on The Sorceress, so we gotta keep her safe

but a Full WCV-Changeling should be as long as they have the refresh to pay for it.

A changeling-WCV, yes. Full fae-WCV, no.

If you extend a reactive evocation block does it function like a normal block from that point onwards so that you can use other skills if it is bypassed.

Yup. But remember that extending it, just like regularly casting a Block, is a standard action. You can't extend and attack at the same time. Mind you, according to the sidebar text, the reactive block lasts until the end of your NEXT exchange, so you wouldn't necessarily need to extend it on your next action.

If feel that I have received some very good and constructive feedback on the question about reactive evocation blocks. Two questions remain (for me):

1) In case the reactive evocation block is bypassed by an attack – is the practitioner allowed to throw up a second one (I would say yes, costing another bunch of stress...)?

2) The reactive evocation block replaces the practitioners normal defense roll - would it mean that the defense value for a second attack, if the block is bypassed by the first, equals a) the practitioners Athletics-value (i.e. value, no roll), b) defaults to Mediocre (he is not allowed to defend at all) or c) is the fact that the reactive evocation block replaces the regular defense only applicable to the actual attack triggering the reactive evocation block (given that the there is a second attack and that the first bypasses the reactive evocation block)? I would rule that the practitioner uses his Athletics value for other attacks, but is not allowed to roll (i.e. not allowed to invoke aspects etc).

1) Hellz no! A reactive block replaces another defensive roll. Regardless whether or not it costs another stress, someone can only reactively defend once. Otherwise, someone else could claim that he should be able to roll Weapons to parry if his Athletics roll to dodge a sword blow failed.

2) While you cannot reactively defend more than once against a single attack, you are allowed to defend against as many attacks as you receive. So yes, if your Evocation block fails, you can then defend against subsequent attacks using other (logically used) skills. The only reason to cast a reactive Evocation block in the first place is to simply replace another skill you think might be too weak to defend with.

as devonapple said, summer magic clearly says that it takes care of the problems of using biomancy.

I personally don't put a lot of faith in the stats in our world. i was providing examples in the novels which could have supported this mechanical method.

I actually already responded to your spoiler-ed comment

(click to show/hide)

I don't believe that any level of fae magic will work against iron. doesn't matter if its a block 1 or 1 million.

Not quite. At least not from how I read it. Summer magic makes it *easier* to create those effects because it understands biology, but it doesn't lessen the strain your body takes from the ordeal. In other words, it drastically reduces the complexity requirements and can cast at the speed of evocation to allow you to instantly run at three times your speed by powering up your muscles, but in the end, you'll still end up with badly ripped up legs.