The only way to add a point to a spline in blueprints is to add it at the end; if you want to add a point at the beginning of the spline, you have to put the points into a location array, add the location you want at the beginning of the array, then clear the points and create new ones using this location array. However in doing so, you destroy the tangents. There is also no way to edit tangents through BP. You can get them, but not set them. I would like to see this functionality!
Thank you
-Me