Replacing a Segment of a Path
The Replace tool 
lets you replace certain path parts by lines or beziers. Thus, you can easily change the shape of an object by defining two points on a path and replace it by a line or bezier.
How to replace a segment with a straight line
1. Select the Replace tool from the Tools panel.
2. Click one point of the path as a start point of the replacement.
3. Click a second point on a path as the end point of the replacement.
4. Double-click the end point.
A line is drawn between the two defined points, replacing the original paths.
How to replace a segment with a bezier curve
1. Select the Replace tool from the Tools panel.
2. Click one point of the path as a start point of the replacement.
3. Click a second point on a path as the end point of the replacement.
4. Click the preview line and drag it into a bezier.
A bezier is drawn between the two defined points replacing the original paths.