From here, Legal - Repair Terms and Conditions - Apple
Service done by anyone other than Apple or an Authorized Apple Service provider will render the device unservicable by Apple.
Excerpts:
1.8 Service Exclusions and Diagnostic Fee. (including faulty installation, repair, or maintenance by anyone other than Apple or an Apple Authorized Service Provider), unauthorized modification, extreme environment (including extreme temperature or humidity), extreme physical or electrical stress or interference, fluctuation or surges of electrical power, lightning, static electricity, fire, acts of God or other external causes (“Service Exclusions”). Apple will return your product to you without servicing it and may charge you the Diagnostic Fee.