in the terrain editor, use the keyboard shortcut for 'copy' in your favorite 2d image editor, create a new document and paste. you will, however, lose information - Bryce's terrain editor uses 65536 levels of grey whereas once you've pasted it, it'll only be 256 levels of grey. saving as a preset won't have that problem.

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Check out my Elemental Hexagons deck, created with Photoshop, Bryce, MojoWorld, and Poser