The Replace tool segment 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.
    seg
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.
    replace1replace2
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.
    bez1bez2