Hi there,
I have done this sort of work previously. Here's my experience
1. Few of the things can be achieved easily. But it can be said in every case. Few of the apps are just impossible to modify without spending too much of time.
2. Even if the app is modified, few of them have server side check, inbuilt integrity checks that causes run time crashes.
I can help you in this project to the max I can, but as my experience goes it may or may not work.