Hi Mark,
The Decorative Truss is a fixed object, not editable, except in total height and width. If you change these two dimensions it will change the pitch but you will have to experiment to get the right combination (unless you are good at maths!).
You can of course make your own trusses. Use the forum Search for Truss and Rafter to get directions for how to do it and ask again if necessary.
Allan
