We've created a game modding driver that we call MantaMod, which works directly at the OpenGL ES stream by intercepting it before passing on to the actual vendor driver, allowing for run-time dynamic insertion of textures into games.
Since it works at the driver layer, modding of games such as AngryBirds, CandyCrush, etc, can be done without needing to change the original game package at all.
We're a small team so haven't had a chance to test this on many devices. So if anyone out there will like to download, give it a try, and let us know if you run into any issues / what else can be improved, that'll be much appreciated!
Download it here, and the site has walkthrough docs on how to install / get it up and running: www_mantamod_com
Do note that MantaMod does need a level of developer experience (at least knowledge of how to use adb, and needs your device to be rooted)