Resize all @3x images in a folder to @2x and @1x sizes. Using this script you need only ever edit the @3x images. Drop this script into the folder containing your images and double-click it in Finder to run. Note it will destructively overwrite the @2x and @1x-sized images, so be careful. Don't run this script in a folder that's not under versio…

resizer.txt

#!/bin/bash -e

# Ensure we're running in location of script.
cd "`dirname $0`"

for f in *; do
  if [[ $f == *@3x* ]];
    then
    echo "$f -> ${f//@3x/@2x}, ${f//@3x/}"
    convert "$f" -resize 66.66666% "${f//@3x/@2x}"
    convert "$f" -resize 33.33333% "${f//@3x/}"
  fi
done

echo "Complete"

Worked like a charm, thanks!