Comment by moduspol
Actually it depends. Apple does provide a way to configure your app for certificate pinning, which then allows you to pin certificates without any changes in your code. [1]
Any apps that set up certificate pinning this way could be bypassed by Apple, though obviously there would be little value in them doing it since that'd just lead to app developers doing what you're describing instead.
Though if I'm understanding this correctly, jailbroken phones could probably bypass it by modifying an app's Info.plist and running the app despite the broken signature.