I've implemented undo/redo and uploaded version 1.0 to https://sourceforge.net/p/sweethome3d/plug-ins/14/
I would still advise taking a backup copy of any model before making bulk changes (this code is very new and undetected bugs are always possible).
Thanks again for the info.
Thanks for this plugin 
It would be nice to program undo/redo. It's really not difficult to implement and you'll find plenty of examples in Sweet Home 3D source code, mainly in PlanController class. Once you retrieved the UndoableEditSupport instance with getUndoableEditSupport(), you just have to create an instance of AbstractUndoableEdit, overriding its undo, redo and getPresentationName methods, and finally call postEdit.
It would be nice to program undo/redo. It's really not difficult to implement and you'll find plenty of examples in Sweet Home 3D source code, mainly in PlanController class. Once you retrieved the UndoableEditSupport instance with getUndoableEditSupport(), you just have to create an instance of AbstractUndoableEdit, overriding its undo, redo and getPresentationName methods, and finally call postEdit.
