A couple of days ago, Apple announced that it is widening its Self Service Repair program to cover some MacBooks too. For now, this include parts and repair manuals for the MacBook Air and MacBook Pro models with the M1 family of chips, but Apple has stated that it plans to expand the initiative to Europe and more Mac models later this year.
However, if you were jumping excitedly on the thought of upgrading your MacBook by picking and choosing higher-specced components through the Self Service Repair program, calm your horses.
In its communication with 9to5Mac, Apple's support team has confirmed that any parts you order should necessarily match the original configuration of your device. So, if your MacBook Pro has 16GB of RAM, you can't purchase a motherboard with 32GB of RAM through Self Service Repair.
This validation is ensured by requiring the user to enter the serial number of their hardware and then showing them the appropriate options only. Apple support has warned that if you purchase components that don't match the serial number, your order will be canceled and refunded.
That said, someone could theoretically enter the serial number of some other higher-end hardware belonging to a friend, order a more powerful component, and try to swap it in on their own machine. However, it's probably not worth the risk because Apple has clearly stated that it does not support this upgrade process so you might face a bunch of compatibility issues, at the very least.
Apple Self Service Repair kicked off earlier this year allowing customers fix iPhone 12, iPhone 13, and iPhone SE (3rd Gen) unit by themselves or by taking it to an Apple Genius Bar. Given that it's now expanding to cover more hardware and countries, it's clear that the initiative has enjoyed a decent amount of success.