there's an online android rhythm game that are shutting down soon, so i want to ask if its possible to convert it into offline app and play it offline on my phone.
permission android:name="jp.co.ponos.superstarizone.permission.C2D_MESSAGE" android:protectionLevel="0x2" /
There is no way make online game to offline game except you know reverse engineering. Know assembly is key to modify binary execution. If this is android game, may be you learn assembly for ARM (almost game publisher compile game for ARM cpu, may be you should learn ARMv8 if this is recently game, or ARMv7 if this is old game).
Some game publisher is public their server implementation code for fans host themselves. You could go to their open source repository to find them if they open.