You don't have access to Apple-supplied parts and especially don't have access to Apple-supplied training. Even if Apple did make this publicly available, the o

You don't have access to Apple-supplied parts and especially don't have access to Apple-supplied training. Even if Apple did make this publicly available, the overwhelming majority of people are not remotely qualified to follow along, and making this available to end users just ensures that people will damage their own devices. If you want to risk damaging your device, that's fine, but it just doesn't make sense to demand that Apple then turn around and provide warranty service to a phone that was damaged by an unqualified user opening up their device and mucking with it. Apple should support a phone after a third-party repair if the third party uses Apple parts and is qualified to do so using Apple training materials. The alternative is that Apple should be on the hook for providing at-cost first-party repair within a reasonable distance of their entire customer base around the entire world, but Apple doesn't seem to want to operate enough stores to adequately service the repair needs of all of their customers.