A really long time ago I made a modding utility for Minecraft called RedstoneModder, which has been a page on our site for a while as well. However, on September 3rd it will be discontinued and the download link will be removed. Better utilities are available these days (with a real GUI too!), so it's not needed. But if you really like it, or just want a copy to archive, feel free to download it now at the source link below. Remember, September 3rd is the day.
Source: Minecraft Forums