To make a demo plan in Chief, go to the existing floor plan and turn off everything except the wall outlines. (I have a separate layer set set up this way) convert that to a Cad detail. Change it's line properties to however you want to show the old walls on the demo plan. make it a block and use the point to point move to align it precisely with the walls. Place it on a separate locked layer. Now, whenever you move or eliminate a wall it will show the wall that used to be there. Chief could make this an automated feature, maybe I will suggest that.