Okay, maybe im tired or something, but I may still not be getting it.
So currently when you move left/right, the character actually moves in that direction or just rotates so that it can move in that direction with the forward/backward key?
If currently the character just rotates then I can understand how set rotation, if done every frame, would make you move in the direction that the rotation is set to and not allow you to rotate to move left and right.
But if that is the case, just use another trigger event at the end of the tightrope and make it leave the state that sets rotation every frame.
Sorry if I am totally off topic and just not getting your issue, but from my understanding set rotation just sets the rotation once, unless done every frame. Also it is my understanding that once you leave a state that contains the set rotatiom action- the action has no way of setting rotation. So following that logic; if set rotation disables left/right as you wanted, then transitioning to a state that has not got a 'set rotation' action would return your character to normal.
Or am I just totally noobing out here?