Changing a .txt to a .dwi

[bc008]

I changed a .dwi (UNIX EXECUTABLE) to a .txt so I could edit it. I should be able to change it back to a .dwi, but it wont let me (just stays a text document)
You can do it in Windows, as seen here at 5:11.

http://www.youtube.com/watch?v=YBXLK_kmPXI

 

[harry*333]

select the file in finder
command>I or file>get info
make sure the hide extension isn't checked
delete .txt and add .dwi in the name
press enter and a dialogue box with appear select use .dwi and now you have dwi