Rational Bezier Curve Tool
A tool to add "weights" to Bézier Curve control points as shape parameters
Rational Bezier Curve Tool

Select an existing nonrational Bezier curve or rational Bezier curve from this tool and use Edit as Rational Bezier Curve or Edit Rational Bezier Curve respectively in the Right Mouse Button context menu to activate this tool.

Then to change the weight of a non-end control point, hover the cursor over the control point you want to change the weight of so that it is highlighted in green, type the new weight you want for it, without moving the cursor away from the control point, and press enter or return to influence the shape of the curve.

Other than changing the weights, you can also edit the curve by moving the control points, contol lines or points on the curve itself.

Note that the effect of changing a weight is different from that of moving the control point.

Also, shamelessly plugging a paid extension of mine, you can use the Bezier Curve Manager to modify the curve(s) further if required.