THE Rename version 2.1.6 (dated February 2004) is a donationware designed to help you rename files en masse with a number of possibilities and options.
Rename files, directories, change/delete extensions, change filename case, export tags from music files and tags images.
I use it to rename tif images to a Library microfilm shelfmark number as part of tif checking and management. I have also used it to rename other files when there has been slippage in the numbering and matching process. It is quick and easy and reversible. There is a preview option so you can check one file before renaming thousands.