include a facility to change EXIF data (on photos) in batch mode

Include a facility to change EXIF data (on photos) in batch mode:- I've often got batches of photographs where I might want to alter the original data, to suit MY filing system, rather than the 'standard' version.
Also, frquently, I want / need to add in additional data not captured / added by the camera at the time the picture was taken.