Just found out this problem is called Asymmetric TSP. I'm going to do some reading on this topic.
A quick google search pointed me to: Inver-over Operator for the TSP which seems to be exactly what you're talking about.
It sounds to me like you're trying to write map searching software and you've noticed that the Travelling Salesman Problem when applied in the real world also has to account for one-way roads. You are looking to solve this by representing the problem space as a Directed Graph?
Rather than mutating the data structure to have different distances in either direction, why not redefine the linking structure to support one-way connections? Wouldn't this allow the current path-searching/choosing routines to continue to be used without modification?
Wait! This isn't a Parachute, this is a Backpack!