Use the Part Browser to select a 3D model to associate with a feature class model.
When importing a part, you cannot change defined units. Utility Design uses the Factor value to calculate the scale for the part based on the units for the part and the current drawing. You can only change the scale for the part if the default unit setting for the part is not specified.
You can control visibility and color of the 3D part using the Visible checkbox and the color picker in the 3D section of the Style Editor. For more information about defining styles, see About Styling Feature Classes.