With a plug-in, the only way I can see could be using the setVisualProperty method in Home class. Be sure that all the objects you store there implements java.io.Serializable interface.
Without a plug-in, you will have more freedom but it will be more complicated, since you will have to create a derived version of Sweet Home 3D, by subclassing SweetHome3D class, to override its getHomeRecorder method and return a different HomeRecorder instance. If you go that way, you can also override createHome to return a Home subclass instance of your choice.