[dnanian]

You'd need to create two files -- plain text ones -- with those commands in them. The actual files would be:

saveicon.sh:

#!/bin/sh

# Save volume icon

if [ -e "$4/.VolumeIcon.icns" ]; then
   cp "$4/.VolumeIcon.icns" "/tmp/$3.VolumeIcon.icns"
fi

restoreicon.sh:

#!/bin/sh

# Restore volume icon

if [ -e "/tmp/$3.VolumeIcon.icns" ]; then
  cp "/tmp/$3.VolumeIcon.icns" "$4/.VolumeIcon.icns"
  if [ -e /Developer/Tools/SetFile ]; then
    /Developer/Tools/SetFile -a C "$4" # Set "custom icon" flag for volume
  fi
  rm -f "/tmp/$3.VolumeIcon.icns"
fi

These would have to be saved in those files, then each would have to be marked as executable. That would involve a command in Terminal (assuming they're in your Home fodler):

chmod +x ~/saveicon.sh ~/restoreicon.sh

Thanks for the other comments.