I want to perform the action of creating a new material in a macro.  Manually this is done by Right-Clicking the part and selecting "Material" -> "Edit Material".  In dialog box I want to navigate to  "Custom Material" -> "Plastic"  and right-click -> "New Material".  How can this be done with a macro?  I have only been able to find places where I can apply an already known material to a part, not one where I can define the material then apply it.