There is a program called "Bryce Librarian" available at wolfiesden.com which allows you to swap preset library files in & out of the Bryce presets "on the fly" while working in Bryce. I've used it ever since I was on Bryce 3. I have about 50 different preset library files and swap them in and out of the "Boolean, Mountains, Tutorial, & User" categories all the time. I have the library files in the "storage" area organized by type of prop, i.e. about 2 dozen for different architectural elements, several for trees, etc., and so forth. I've found that by dividing them by class and having lots of libraries I can keep the size of each individual library obp down to around 50 Mb - makes for quicker swapping and doesn't eat so much memory when loaded in Bryce. Until I can afford a new computer and upgrade to Bryce 5 to get the library structure available there, this is the next best thing. It does objects, mats & textures, but not skies.