The Make Spline Point function takes an Input Key parameter. However the only functions that use a Spline Point Structure are “Add Point” and “Add Points” (taking an array), and these appear to only add to the end of the Spline Point list. As such, it looks like the only way to use Blueprint to set Input Key is to loop through the spline points by index, and create new SplinePoint structures from them, then Clear Spline Points, and then Add Points. 