How can I change a file or folder icon using the Terminal
You'll need the Developer Tools installed, and then the following might work. This takes the graphic in icon.png and applies it to file.ext.

# Take an image and make the image its own icon:
sips -i icon.png

# Extract the icon to its own resource file:
/Developer/Tools/DeRez -only icns icon.png &gt; tmpicns.rsrc

# append this resource to the file you want to icon-ize.
/Developer/Tools/Rez -append tmpicns.rsrc -o file.ext

# Use the resource to set the icon.
/Developer/Tools/SetFile -a C file.ext

# clean up.
rm tmpicns.rsrc
# rm icon.png # probably want to keep this for re-use.