Animation direction of a LineRenderer

In a LineRenderer script, I would like to change the corresponding animation direction of the LineRenderer. As far as I know the animation always runs from start point to end point. Now there are several cases where the animation direction should be changed. For one case I can adjust the animation direction directly in the Start(). For this I wrote a method ChangeAnimationDirection() which simply swaps the current start and end point. This also works without any problems.
Now to my problem or my question. I have to change the animation direction also at the “runtime of the LineRenderer”. So I call ChangeAnimationDirection() from Update(), the points are also swapped, but the animation direction does not change anymore. I have also tried to use a coroutine instead of the Update() method and call ChangeAnimationDirection() from there, without success.
Can someone answer me how to change the animation direction at “runtime”?

//works
void Start(){
if(…)
ChangeAnimationDirection();
}

//doesn’t work
void Update(){
if(…)
ChangeAnimationDirection();
}