This repository has been archived by the owner on Sep 23, 2018. It is now read-only.
OS X El Capitan introduced a new security policy preventing users from changing any system icon.
However, you can still continue to change your apps and volumes icons normally.
Apps like LiteIcon still work pretty well for this sort of thing, but it requires a lot of manual dragging.
If you're like me and enjoy using the Terminal to automate work-flows, I think you'll enjoy what's to follow.