It's common to tweak your @2x images. You might not want to spend double the effort to tweak the normal version of your images especially when you know that you might be tweaking them again. If you install ImageMagick, here's 2 handy commands that will help you generate the normal version of the images from your @2x version. Be careful they override any existing normal images. In a terminal,
cd to your project directory and run:
find . -name "*@2x.png" | xargs mogrify -format PNG32 -resize 50% find . -name "*@2x.PNG32" | sed -e "p;s/@2x.PNG32/.png/" | xargs -n2 mv
 You can install ImageMagick using Homebrew.