[dnanian]

Well, a 'dset' is a copy script, not a shell script, so I'm not sure what you created there. In general, you'd create a plain text file that would look like:

#!/bin/sh
defaults write /Library/Preferences/com.apple.TimeMachine "$1" -boolean no

Where $1 is the name of the source volume, as explained in the User's Guide.

You'd save that, probably with a .sh extension, and then you have to use terminal to set its permissions to allow execution, i.e.

chmod +x /path/to/the/shell/script