How to access to the iOS system files WITHOUT jailbreak?

I'm an iOS developer and I wanna know if there is any way to access to the iOS system files without jailbreak. I believe this is definitely viable , just how?
Here is the story that I said these words:
There is an APP lunched by an enterprise account, it can do one special thing with or without jailbreak. I want to know how, so I used the SSH in a jailbroken iPhone and found that it modified one system file in this path(/private/var/wireless/Library/Preferences).
Here is the latest progress: I decompilate the APP and find it used these third-party library files: libobjc.A.dylib, libSystem.B.dylib and libcucore.A.dylib, these library files are used for jailbreak. So I guess it may use some system hole to do this.

Thanks very much!