I thought iPhones have some kind detection if parts are changed and it simply stops working.
That being said, I doubt Apple is going to track it down to such a degree but the screens and the batteries and everything are serialized. They could follow the parts into individual phones if they really wanted to.
> Apple’s own anti-theft measures appear to be working, as The New York Times reports that police in New York, San Francisco and London are finally seeing a decline in theft of the iPhone. The introduction of Activation Lock on iOS 7 has seen iPhone robberies drop 38 percent in San Francisco, 24 percent in London and 19 percent in New York, based on the six months before and after Apple released the feature…
And that's nine years ago.