Crazy Hand is a character editing program with many, many uses. You can modify character attributes, swap animations between subactions, change hitboxes and attack properties, and even edit frame data.
NOTE: Crazy Hand is a Java program. This means that it is a JAR file and not an EXE file. Programs like WinRAR will try to open it like an archive, but you want to open it as if it were an executable and find your Melee ISO. To do so, right-click and select Open With -> Java Platform Binary. From there you can select a character and begin modding.
Don't forget to press the Save button at the bottom of the window after every change! Crazy Hand does not keep track of your work when you move between categories. I would also recommend creating backups of character files using DTW or even your ISO as a whole.