Do Lines support scripting?

Scripting is supported. You can display an overview of MAXScript properties with the function showProperties(). Use the following to show an overview of the Line properties.

showProperties(Pencil_4_Line())

You can also use MAXScript Listener's Macro Recorder to see how properties are changed when performing operations on the graphical user interface.
Please have a look at the script samples in the Tutorials section.