Within iPad and iPhone apps the apps are what is called Sandboxed, this basically means that you cant interact with them from other apps on the device or via a pc. The apps therefore get all their updates provided in app either through in app purchase or through a full update from the app store. This means that you can't upload your own files in to it.
So sadly you won't be able to make any updates or amendments to your copy of Tom Tom unless Tom Tom want you to and if this is via an in app update then Tom Tom will charge you for the pleasure.
Tom Tom with iPad
