Using Replace Offsets
Use the 
Replace option to replace a specified surface on a solid with a datum plane or quilt. A surface replacement differs from an extrusion or a cut because it can add material in some places and remove it in others.
Replace option to replace a specified surface on a solid with a datum plane or quilt. A surface replacement differs from an extrusion or a cut because it can add material in some places and remove it in others.Quilts used to replace surfaces are consumed by the replacement feature unless you click the Keep replace quilt check box on the Options tab. The Keep replace quilt check box is not available when you select a datum plane for the replacement operation.
A quilt that has replaced a feature's surface cannot in turn be replaced by another quilt. The replacement surface must be deleted first.