Having worked for another company in the past, namely Sony Mobile, most of what I have been doing in Android stemmed from my previous experience.

Not only was I part of Sony's core overlay testing team (as well as theming engine) back in Android 4.4 (KitKat), I also started a community of themers called chummy development team back in 2014, of which created themes and stepped beyond boundaries of what Android allowed you to normally touch through overlays. I also created app add-ons that hot-swapped resources on-the-fly!