DISCLAIMER copyright claims are n easy thing!
1. "server sided apk", can't be hacked, at least you have to hack the server itself, depending on what data you want to modify and where the data is computed - on client or host side.
(tried something similar with the ingress apk
2. to modify an android application you should have programmed one at first - or know about the structure of such an app, for reengineering purpose.
2.2 yes this the heavy load, what to do now depends on what app you want to modify and what in the app - up to you!
Sent from my Nexus 4 using xda app-developers app
Keep Calm, and push the THANKS