To Modify a Material Definition
In the Material Editor dialog, select a material from the Material drop-down menu.
Settings for the selected material are displayed. The material is displayed in the Display area.
Make required modifications to the material's settings.
The Display area updates to display the current material. The original material is replaced by the new definition, and will be used in the next render. Where an external material palette is open, a local material is created of the modified material.