Search Replace Transfer
Search Replace Transfer is a Lightroom (version 2 or greater) plug-in designed for bulk changes to text in Metadata Panel fields.
The plug-in also provides a number of custom fields where you can store metadata which doesn't fit in EXIF or IPTC fields, and a mechanism for copying metadata from iView Media Pro.
Search Replace Transfer works on Lightroom 2, 3 and 4.
Payment and Updates
The trial version operates on up to 10 images at a time. Purchasing the plugin will give you a registration code that will remove this restriction. All future updates are free.