Previously, if you had replaced your damaged display or taken it to a cellular repair shop to do the repair, Apple would not authorize any repairs under warranty.
Here's how it works now:
When a customer with an iPhone that has a third-party display seeks a repair for a non-display issue, Apple Stores and Apple Authorized Service Providers have been advised to inspect the device for any fraud or tampering, and then swap out the device or replace the broken part based on Apple's in-warranty pricing.
If a third party part causes the repair to be unsuccessful or damages the iPhone, customers will need to pay the out of warranty cost to replace the part or the entire device if necessary to resolve the issue.
Apple Authorized Service Providers will still decline to service any iPhone that fails related to a third party aluminum enclosure, logic board, battery, Lightning connector, headphone jack, volume buttons, mute switch, sleep/wake button, and certain microphones.