The GNU Project has a great graphic of a meditating gnu which I much prefer over the standard Emacs icon. So I took the PNG file and opened Icon Composer to create a new icon set.
Then I went to my trusty Emacs in Finder and right-clicked it to display the package contents and replaces the Emacs.icns in ‘Contents/Resources’ with the icon set you find here (Meditat.icns)
Your Emacs will now sport the following icon in Finder (might take some time due to image caching and such, I dragged it to the Dock and it worked instantly)..
