helpme

Basically I want to know if it's possible to make an app that replaces an file in the root directory of the phone, with a file that I can inject in the app itself. Here how I'm imagining it: In the app to be a option where I can select a file. Then have an option to select the file to replace.

i know how to make bo2 mod menu and modding stuff on ps3 but this is new to me can some one help me to get started and what do i need to start modding/hacking app or does some one know a good video tutorial just for the basic's i have never workt whit this im used to work whit c++ not whit c#...