My answer would be that in Dresden Files, you actually can't use magic to grant yourself a temporary skill, but rather a specific spell effect limited to a specific application of a specific trapping.
I could be wrong though, as just because I haven't found an example in the books of a Spell granting temporary access to a full skill, doesn't mean that the example doesn't exist, as that Core Rule book is a "brick" (400+ pages) and finding things in it is difficult at times.
I personally would say that granting broad access to a skill based on shifts of power would be a slippery slope and would cause some potential game balance issues.
A Stunt (and by extension Refresh) is useds to add a new trapping to a skill. Essentially letting the character do things with one skill that that normally couldn't be done with that skill.
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 Magic to replace other skills you don't have would seem pretty difficult, but not probably 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.