Changing iOS app icon I want to change the app icon for a pre-installed iOS app. What are my options?

Is there a way I can download an .ipsw file, change the icon of the app in it, then change something to make iTunes think it is newer than the version currently on the device, so it can apply it as an update, so all my data on the device will not be removed? (Which would happen if I applied it by restoring with it.)
No.

It is not possible for a user to change app icon for any iOS app, let alone system apps.

iOS doesn't allow users to tinker with .ipsw files and have them installed. Making any change to the app bundle would alter its signature and there would be no way for the system to verify if the app came from the original developer.

This idea is one of the major foundation for iOS security.