This plugin can be used to make site wide changes it allows you to dynamically (i.e. at the time when a page is generated) replace code and text from themes and other plugins with code and text of your choosing before a page is delivered to a user’s browser.
Because the find and replace happens in real-time no changes are needed to plugins or themes which means upgrades remain easy!
It works without modifying themes or plugin files.
It is reported to be running on version 2.9.1 without any problem.
Plugin Homepage: http://www.mariosalexandrou.com/blog/real-time-find-and-replace-for-wordpress/