So what, I considered, would really come of a con man learning magic?
He could, of course, decide to scorn it as cheating, or think it might make him slack, or any of a thousand other reasons to reject the notion, but what if he did? Had some motive to learn it?
Would he prefer illusion magic to make more skillful cons?
Or would he prefer magic that is not intended to be illusionary? Because you can bet that his trick will be to find ways to bend it to do things that it's not intended, to make them seem other than they are -- and preferably greater. Character is not fundamentally altered by knowledge alone.
Hmmm. . . that's a notion that would need some serious development even before you fit it into the plot.
Probably not an accident that in Willow, where a sleight-of-hand artist learns some real magic, the climax of the story turns on his feigning to use magic when he's actually doing sleight of hand.