@goofy: Access the Preset Object Library by clicking the right facing arrow to the right of Create on the top palate. Another window opens with the title of Objects. Along the left side are headings for different objects loaded into Bryce. Near the bottom are a minus and plus sign, to the right Add/Delete/Import/Export.
Whatever OBP you have can be added to this library by clicking on Import and placing the object in whichever category you want—whichever one has the most open boxes. Or, using the Plus sign creat a new category that matches the object you want to add. Just make sure the title you chose will help you find that object(s) when you want them.