I usually have the polyline deleted when I select the object to grade from, on the screen that pops up after selecting the object there is an option to delete the original line.
I usually explode the grading object and add the feature lines. Sometimes I just paste the grading surface into my design surface, create a snapshot of the design surface and keep the grading in the drawing. I usually explode if I don't think I will need the grading again, and the snapshot if I think I will. The snapshot ensures I have a copy of the grading in my design surface even if the grading goes awry.
Christopher
http://civil-3d.blogspot.com/
Civil Reminders
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