Automation rule script help

[Shankar Dharmaraj]

I am trying to write a script to have one of my custom fields to have these values

Its a drop down list 

The custom field i am trying to edit is customfield_10029 (from the page: editCustomField!default.jspa?id=10029)

I want it to be these 2 values in the future (cascading select searcher) / edit options for custom field

selectedParentOptionId=10026 

and another option under that is selectedParentOptionId=10026&selectedValue=10182

Can someone please help me write the script to get this automated