Hmmm...in bryce 4...I have bryce 5 and there is a way to do this so it may work in version 4. Go into the bryce folder under presets and look for a file called user.obp or user.mat or user.bsk depending on which area you are in. Then just duplicate that file and rename it and the new category will be made in the appropriate folder in bryce. Then just re-add all of your presets into the right category (can take a while) and delete the old ones. Dunno if this works but have a go anyway :)