In order to define a contextual action for seismic histogram layers, you need to put your Python script in your Python directory under a directory called Contextual_Histogram_Seismic_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 seismic histogram layer:
This script will reduce the selection area of the histogram by half.
The script is attached to the bottom of this article.
The result after the script executes should look something like this: