>How can I edit out the hatching on the rib?
As indicated by Dennis you can RMB turn off the hatch. Then Project Geometry the edges and draw lines for the correct ANSI standard boundary. (You have to RMB Done after projecting the needed edges.) You can then re-apply your own hatch to the newly created boundary.
I saw a demonstration of the forthcoming SolidWorks 2008 do this correctly without all of the manual editing.
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