Community Tip - Did you get called away in the middle of writing a post? Don't worry you can find your unfinished post later in the Drafts section of your profile page. X
How do I edit the endpoint arguments to a spline? For an example, I want my spline to start perpendicular to a line in my sketch or if I want my spline to start in the elongation of a line?
The only modifier is the tangent modifier, which would apply to extending a line. To be perpendicular, create a construction line that is perpendicular and make the spline tangent to that.