Key Replacement

Depending on your model of MacBook, Apple will likely not replace the keyboard on your Mac. Macs introduced in 2016 or newer require the entire top case to be disassembled to replace the keyboard, and no one singular key can be replaced. AppleCare+ also doesn't cover cosmetic damage if your device functions normally.

However, you may still be eligible for a free replacement if your MacBook Pro was introduced between October 2016 and July 2019. If your Mac is one of the models listed on this site: Keyboard Service Program for MacBook, MacBook Air, and MacBook Pro - Apple Support, then you may be eligible for a free replacement.

Lastly, Mac repairs often take time, sometimes over 7 days, so if you use your Mac for work, I would highly recommend simply ignoring any cosmetic damage if it doesn't interfere with the functionality of the device.

In theory Apple or an Apple Authorized Service Provider should be able to just replace the worn key caps, but I don't know how it would be priced. However, I would not expect it to be real inexpensive since Apple doesn't make it easy on the AASP since an AASP must purchase an entire set of key caps for the whole keyboard. The AppleCare+ coverage would make the repair cost $299 US which I don't think is very cost effective for key cap replacement (probably will replace the entire Top Case/Keyboard Assembly). I don't know if the worn keys would be covered for free by the extended warranty, so this is a question you would have to ask Apple or the AASP.

Chances are the key caps can be purchased from a third party vendor, but most Apple laptops use at least two different types of key caps (and mounting mechanisms) so it can be difficult getting the correct key cap for your laptop. With the USB-C Macs it can be even harder since there can be different shades of black on the key cap which can really be noticable when installed next to a different color/texture of black key cap. Plus the USB-C Macs may have different symbols on the specialized keys depending on the exact model of the laptop and when/where it was manufactured. Plus it is very easy to damage the key cap and scissor/butterfly mechanisms. If the Butterfly mechanism is damaged it will require a whole new Top Case/Keyboard Assembly.