APK modification script

What i need is a script that can modify an apk like this : I have the [login to view URL] file. In this file i have an [login to view URL] file. I want a bash ( linux ) script / program , that will do the following : - unpack the apk to a folder - replace the [login to view URL] file in that folder, with a given [login to view URL] file - re-pack the apk , sign it, but the most important thing, i want to keep the same signature if i make 3 changes, so i can update the app on android device. Job is pretty straight forward, and i want to test it before i pay.