Most of the time they will decline to touch it if you had an unauthorized repair. But if they do work on it they are not responsible for any damage that may occur in the repair attempt even if it’s covered under warranty (the warranty pretty much becomes null). They may contact you and give you the opportunity to pay more for the damage that occurs if they are to fix it and if you refuse the charge they will give you back the damaged device without being responsible for anything.
1.11.6 Disclosure of Unauthorized Modifications and Non-Apple Service. During the service ordering process, you must notify Apple of any unauthorized modifications, or any repairs or replacements not performed by Apple or an Apple Authorized Service Provider (“AASP”), that have been made to your product. Apple will not be responsible for any damage to the product that occurs during the repair process that is a result of any unauthorized modifications or repairs or replacements not performed by Apple or an AASP. If damage results, Apple will seek your authorization for any additional costs for completing service even if the product is covered by warranty or an AppleCare service plan. If you decline authorization, Apple may return your product unrepaired in the damaged condition without any responsibility.
Legal - Repair Terms and Conditions - Apple