You'll need to remove the cylinder you already added to see the new clinder you add with a smaller radius:
Code:
import viz
import vizshape
viz.go()
viz.MainView.setPosition(0,0,-4)
slider = viz.addSlider()
slider.setPosition(0.2, 0.1)
slider.set(0.1)
myshape = vizshape.addCylinder(height=1.0,bottomRadius=0.5,topRadius=0.1)
def changeRadius(pos):
global myshape
myshape.remove()
myshape = vizshape.addCylinder(height=1.0,bottomRadius=0.5,topRadius=slider.get())
vizact.onslider(slider, changeRadius)