In order to define a contextual action for pointset histogram layers, you need to put your Python script in your Python directory under a directory called Contextual_Histogram_PointSet_Layer.
Go to Tools->Options->Environment->Python Scripts (or Tools->Options->Python->Scripts in INTViewer 5.2) and click "Refresh from Disk". Your script should be listed automatically.
You will now be able to execute this script from the contextual menu of the pointset histogram layer:
This script will add another histogram layer with twice the number of bins into the same window as the current histogram layer.
This script is attached to the bottom of this article.
The result after the script executes should look something like the following.