Is possible to change an app icon on 4.1 on my S3?
Unicon
is an icon theming tool which requires root, but it's more consistent throughout the      device.
Icon Changer changes only the icon of the shortcut, but doesn't require root.
Use Apk Extractor to get the installed apk from the device, transfer it to a PC, modify it and then reinstall it. Does not require root.