Archive Cracking.

I need help cracking MapleStory's .wz archive.
You can extract stuff, but I haven't found a way to add stuff to the file.
Can anyone help me?
Here is a file if you want to try it.

why dont you extract and repack with winrar winzip 7zip and see if the game recognises if you change the extension otherwise you can look for a file analyser to work out the packer used