alied's tip is good but I just have some doubts about classpath when opening homes with substituted objects, and how undo/redo will work when you substitute an object by an other one. At the minimum you should take care of the index of the added piece.
An other tip is to manage all your additional information with setVisualProperty/getVisualProperty methods available in Home class. It won't be a very clean architecture, but will work out of the box if you store there only standard class instances.