Open the editor in the Tools menu. Create a new file there. Go to the Wondrous Items tab in the editor, and at the bottom left, select "New (Copy)". Choose the luckstone from that list, and write down the unique Id that's listed with it on a piece of scrap paper. (The Id runs off the right edge, but it's "ioStonLuck"). Now that you have a copy of the item, change the name, and enter a new Unique Id, like "ioStonLucA".
Now, if you want this new name to override the existing name for every instance of the luckstone, find the "Replaces Thing Id" field on the center-right of the editor, and enter "ioStonLuck" there. If you want your new name to become a new magic item that will exist alongside the current version, skip that step.
Now, save your item (and the file if you hadn't done that), and press the "Test Now!" button on the top left, and your replacement/addition will be available in HL.