There are several applications which will edit the EXIF data of various camera's RAW formats.
I can think of many reasons one might want to do this. For example, if using CS2 for HDR it will not let you buid an HDR image out of one RAW file processed two or three different ways. However, if you edit the exposure in the EXIF then CS2 churns out an HDR.
Here's a post on another board with several of the pieces of software listed that do this.http://www.outbackphoto.com/workflow/wf_82/essay.html