Simply put, Hedge Magic is totally up to the Narrator. Hedge Magic is the magic of the Empire City Epoch. It is published in countless volumes of witchcraft and ritual magic, most of which are meaningless, mumbo-jumbo crap. Whether or not these things actually work... Well, according to most of "civilized" society: No, it doesn't. However, enough people believe in the possibility of magic, and even more practice it, that some effect may be elicited through these "modern" rituals. The limitation of Hedge Magic is that it is inundated by mundane reality, and therefore may only be used to alter probability in unremarkable ways.
For Example:Bobby wants a job so he casts the "Neidajawb" incantation on page 57 of his Cute Lil' Book 'o' Spells. The effect of his strong willpower bends the probability in his favor, but only if he goes out and looks for a job. He does indeed find work. The spell either worked or he simply got a break through virtue of the power of positive thinking.
Will Roll, Difficulty assigned by Narrator
This is the "magic" of luck. It occurs on a case by case basis, by pure random chance for reasons totally unknown by both the accidental practitioner and scholars who have spent time studying the phenomena. Those who experience the effects of Incidental Magic, the occurrence of the seemingly impossible, may waken to the reality of the existence of True Magic.
This sort of thing is utterly in the Narrator's hands. Inexplicable good fortune in the face of impossible odds (usually to save the entire party from meeting a tragic end due to a poor decision) is the sort of thing we are talking about here. Narrators should not abuse this sort of power, as actions should have consequences.