How to modify Google Apps?

Hey Guys,

I have an Nexus 4 I wanted to look around in Reverse Engineering... So I installed Virtuos Ten Studio and imported NetworkLocation.apk, However compiling it back gives me error because of a wrong certificate (something with shared user id). What do I need to do to modify Google Apps?

I have already resigned my Rom and the Gapps Package (AOSPA)

Thanks for your help!