change app. and drive icons
you need to make sure that the you have entered in recovery mode terminal: csrutil disable. restart computer and instead of the select all .icns files in preview and copy and paste the icon over to the inspector using command + v, you just drag the completed .icns file on top of the existing inspector icon and then pull up terminal and: killall Dock or just one the app. hope this helps.
MacBook Pro with Retina display, macOS High Sierra (10.13.3)