Xiafunge is a utility for changing the extensions of files. You may drag one or more folders (or files) on top of the application in the Finder or the main window, and the program immediately begins to traverse the folders and all their subfolders changing the extension of all files that match the "from extension" to the specified "to extension."
If the "from extension" is blank Xiafunge will append the "to extension" to any file without an extension.