In the Flash library, you can only duplicate the items one at a time. If you select a folder or more than one item, the duplicate command in the right-click context menu becomes disabled. When you have a bunch of symbols you wish to duplicate, it can quickly become a boring, repetitive clicking job (plus creating folders and drag and drop).
If you wish to duplicate folders in the library, here is a Flash MX 2004 jsfl extension you can install:http://ghostwire.com/files/DuplicateFolder.mxp
This extension was initially created to help in the task of duplicating skin symbols when using GhostWire Components. But the command can be used in any situation where you wish to duplicate folders in the Library. With this command, you can now duplicate all the symbols (and nested folders) within the currently selected folder in the library at once.
After installing the .mxp file, you may access the command via the pulldown menu of the Flash IDE:
Commands > Duplicate Folder
If you use this command to duplicate the skin symbols when using GhostWire Components, please remember that the command does nothing more than just that - duplicate the symbols. When you are editing a copied symbol, remember that the nested movieclips within will still be using the original symbols - this may or may not be what you want. You may use the "Swap..." button on the Properties Panel to swap the currently used symbol(s) to the one(s) you wish to use.