This app will let you conveniently switch out the emoji in your system. Currently available free emoji are Google (stock), Samsung, LG, and iOS. For a small charge, Twitter and Emoji One are also available.
Thanks to gonsa from XDA for providing the font files: forum.xda-developers.com/showthread.php?t=2618523
Busybox is recommended, and the app is untested without it.
Emoji Switcher (root)
Emoji Smiley Apps