InstancedMesh with variable number of instances

Wow, this InstancedMesh is a great addition to ThreeJS.

But I would like to know how can change the number of instances shown on the screen. How to add a few, how to delete some of them.

I figured the count parameter is the max number, but can I vary the number of instances that are really used, like you can with the maxInstancedCount of the InstanceBufferGeometry?

Check out how in this example the count property is used to vary the number of rendered instances.