Is there any simple way of creating tappered thread in OpenSCAD? I need something like 10 mm in diameter at the end, 9 at the top and the height of 10 mm.
If your math and OpenSCAD skills are superior to mine, you may be able to make use of the OpenSCAD Metric Nut, Bolt & Threads Library located here: OpenSCAD Metric Nut, Bolt & Threads Library
It uses various means to generate polygons about a radius and includes the formulae for partial revolutions. It is presumed in the design that the center of rotation for the generated polygons is constant. I looked over the code for outside thread and could easily determine the radius references.
With proper coding, you could generate a variable radius based on the height of the cylinder at a specific point and achieve the tapered effect you require.
I expect that you'd have to reduce your desired radius by a fraction, say 0.05 mm in order to embed the thread forming polygons within your tapered cylinder.
If you aren't a strong coder, disregard this answer.