FogBugz lets you do almost anything to a bunch of cases that you can do to a single case. Simply set up the filter to include all the cases you are interested in, go to the list page, check off the cases you want to manipulate, and click on the appropriate action button at the bottom of the screen.
Alternatively, you can perform the same operations via the case list context menu, accessible via a control that appears when you hover over a case entry in the list.
