(New in developer version. Exists since 30c236f from 27.04.2010)
With the find and replace plugin you can easy change a string in all contents.
You find the plugin here:
If the checkbox "simulate" is checked, the plugin will not changes anything. It only display the changes in a diff view for every items. So you can easy check the operation results.
If the CPU time is limited and the replace operation takes to long, you will get a server timeout. You can find a work-a-round in the related trac ticket
Any Questions about this plugin? Check the related forum topic