1. Using the Rectangle tool - draw a rectangle (notice you can specify rounded corners in the propoerties module below
2. Double click on any of the four corner points of the rectangle and it will convert to a path (notice no ability to specify rounded corners)
How can I convert the path back to a rectangle so I can round the corners in the properties module (not by hand)?
Have you tried undoing the step? That'd be the easiest way. When you try to edit the corners of a rectangle, FW asks if you want to ungroup the shape. Ungrouping the rectangle is what removes featues like the corner radius.
That said, once the rectangle ahs been ungrouped, you can use the Path panel to sharpen or round corners.
If the corner is already sharp, select it with the Subselection tool and fromthe Path panel, choose Fillet points from the Edit points section of the panel.
If the corner is rounded, select both points with the Subselection tool and choose Sharpen Points.