When you define/modify the structure of a stacked wall type, you indirectly change instance properties of the individual subwalls that compose the stacked wall. When you specify the height, offset, top, and base of the stacked wall’s subwalls in the Edit Assembly dialog, you are also specifying the corresponding instance properties of the subwalls: Unconnected Height, Location Line Offset, Top Extension Distance, and Base Extension Distance, respectively). The only instance properties you can directly specify for subwalls are Room Bounding and Structural Usage. The remaining properties are inherited from the stacked wall type and are read-only.
To access the instance properties of a subwall within a stacked wall