Hello Dan,
If you are using the default VB Operator Interface that is shipped with TestStand, then you can set this option exactly as you do in the Sequence Editor. If you are creating a custom Operator Interface, you can set this option using the DisplayRunTimeErrorDialog (or DisplayRunTimeErrorDialogEx) method of the engine. This will display the dialog box that is shown in the Sequence Editor. You would implement this feature in the case that handles the BreakOnRunTimeError UIMessage. You should examine te code of the default VB Operator Interface to see how this is done. Hope this helps.