So you will now have to intercept the server communication.
You can sniff the packets with SandroProxy and possibly write a Plugin for it to "hack" the game.
Sandro Proxy: https://play.google....ndroproxy&hl=de
Plugin Tutorial: https://code.google....detail?id=31#c3
Data is send in JSON Format, the Response is gzip encoded.
You can possibly modify prices and in PVP you could probably edit the damage you do against your oponnent. Thats what I found by looking at the Respone Data you get from the server.
There is also a request happening to "appclick.co/PublicServices/..." where a value IsHacked=false is send to. If you want to modify the .apk itself you should probably deny access to these url or be sure to intercept every case of "IsHacked=true"