Select a folding line of a shape edited element and convert it to a split line. 
You can convert folding lines to split lines in or out of the shape editing mode. 
- Hover mouse pointer over a folding line of the element. 
  
- Press Tab to cycle selection to the folding line. 
  
- Select the folding line. 
  
- Click Modify | <element> tab Shape Editing panel Shape Editing panel  Convert Lines. Convert Lines.
Note: Only folding lines can be converted to split lines. Split lines being converted to folding lines is not supported.