After it was reported that proprietary diagnostic software was needed to replace critical parts on computers equipped with Apple's T2 chip, iFixit decided to put that claim to the test by replacing a part on a brand-new 2018 MacBook Pro. They found that after pulling it apart and replacing the display, it still worked - even without the software.

It would appear that  any "secret repair kill switch hasn't been activated -- yet". So far, it has limited approaches that limit repairs based on security to the TouchID and FaceID sensors that require specialised software.

While it's possible that a future software update could change things and make it require specialised software that only official Apple Stores and authorised service centres have access to, it has not done it yet. Unless of course it has activated it but they put the same crack team on the project which designed Apple's clock software which could not adjust to summer time or time zones.