[RPG] Dresden Files RPG: Can Spells Mimic or Replace other Skills

I haven't found the section in the DFRPG Your Story Core Rule book that specifically talks about if a Spell could fully replace Skills. Can anybody point me to the specific section in the book that shows an example or details of a Spell Effect granting a full Skill Rating for the Spell Duration (either Evocation or Thaumaturgy)?

I have the following issue I'm having a hard time making a ruling on the below Player Request.

Example: I have a player that wants to brew a potion: "I Know Kung Fu". He's got a Lore of 5 with a Crafting Specialization and wants the potion to cause the Mild Mental Consequence of "Badly Dubbed" (spell side effect of not being able to speak clearly and on a delay). With Lore of 5 + 1 for the Specialization and Tagging the Consequence for an additional +2 it results with a +8 shift effect that could be reduced to +7 and last for one extra exchange. Therefore the imbiber of the potion would get a Skill of 7 in Fists lasting for 2 exchanges.

My knee jerk reaction was to rule that the spell could not work that way, but struggled finding details in the book to say a definitive yes or no, and while I will make a ruling based on my judgement, I also endeavor to backup my rulings with details from the core rules whenever possible, and want a run a game where I say "Yes you can" more than "No, that can't work that way". —Thus, I don't know what to do. The Rules as Written in the Core Rule Book are at times pretty obscure, and I don't know if this is an instance of if I should institute a new House Rule.

I found the following Question/Answer:
What good is magic if your skill is better?
—but didn't see that any source material from the Rule Book was quoted, thus I'm speculating about the ruling in that Q/A and I'm currently leaning towards not allowing a Spell Effect to replace a skill for a number of reasons.

1. Primarily, the Skill Limit on the game is currently at Superb and having a spell that breaks that limitation just seems imbalanced. -Why should a spell caster be able to be better (albeit for a brief instance) at martial arts than a Kung Fu expert that has studied her whole life and skill only has a base Fists Skill of 5?
2. Also, it seems to step over other game balance boundaries as well. Essentially, the caster with a high Lore is generating more effective skill with a Skill Trapping not associated with it by running a shell game of sorts.

My current ruling will be: Maybe (based on feedback below). (I'd prefer to be pointed to some source material that more clearly defines the subject)

My Reasoning in addition to what is above:
A Stunt (and by extension Refresh) is useds to add a new trapping to a skill. Essentially letting the chacter do things with one skill that that normally couldn't be done with that skill.

Using a spell to give you access to another skill at a high value or for attack for more than just an instance is out of balance with the above game mechanic in my opinion.

I may allow temporary access to some effects in the same way temporary powers are gained (p. 92). Thus Spend Fate points to get the power you're seeking. The caveat is that access to temporary powers is to be done in RARE circumstances (See Below). If this is a common function or part of your regular use of power then you should pay the refresh for it.

Otherwise temporary access to power will need to be granted in a similar method to the way the book describes:

"…In rare circumstances, it might be appropriate for a character to temporarily take on supernatural powers. Usually, this happens when a supernatural entity imbues someone with power for a short time in order to take on a threat or fulfill some part of its agendas…"

Thus, using Thuamaturgy to replace other skills you don't have is pretty difficult, but not impossible. Like everything in this game, it's an issue of judgement call based on the
reasoning for the spells use and funciton, and the fate points to spend to be able to access the skill you want but don't currently have.

EDIT BASED ON CURRENT FEEDBACK: I'm planning on "ruling" that Spell Effects to modify or replace skill rolls must be specific in use
or trapping and can't grant access to the whole skill and all of it's
uses/trappings. The effect will last for one exchange plus one extra exchange
per shift of energy channeled for duration unless it is a special
circumstance that makes sense to extend for a longer period of time.
Furthermore, I'll be planning on instituting a rough guideline that a spell can't exceed the skill limit as far as the bonus granted unless the character has a very good reason to and it fits within the story/game. I also intend to be a bit more of a stickler on spell effects that have an attack function of some type as the outline for building stunts advises that attack functions need to be more specific/limiting in the situations where they can be used, as I feel the spirit of that guideline is that attack modifications need to be dealt with carefully.