If you explode a grading object, the projection lines and daylight lines become editable feature lines. You can do this to modify projection lines or a daylight line, then add them to the design surface as breaklines for use in either an existing or new grading.
Exploding the grading object creates a closed polyline that includes the footprint, projection lines, and daylight, so it completely bounds the face. Exploding the daylight alone creates a polyline from the daylight. Whether 2D or 3D polylines are created is determined by the Site Display Mode site property, which specifies either “flatten to elevation” or “use elevation.” On the other hand, you can use the ERASE or EXPLODE command on the footprint, which preserves the daylight as a feature line, but does not preserve the projection lines.