Swap default iOS system font in apps

Question

I'm trying to build an app to install a custom set of fonts for other ios apps to use. Is it possible to change iOS 6 default set of fonts and add a custom set of font that other apps can use?

Answer 1

Custom (non-system) fonts must be included in an app's .plist file and must be included in the application bundle for an app to use them.

Since application bundles are read only, it is only possible for an app to use a non-system font that is included before it is distributed.

Answer 2

No, it's not. Apps basically can't change default configuration (like fonts, background, colors, icons, animations) from the whole OS. You can use custom fonts in your app though.