The key caps are in fact replaceable. The mechanism can be a bit delicate, but if you know where damage can occur it’s definitely avoidable. I can give further instructions if necessary, but didn’t want to clutter my response if you don’t end up needing to know.
There is also a known keyboard issue with this type of keyboard switch, so if you’re looking to replace them because they are stuck, not responsive , or a host of other issues I would [link|https://support.apple.com/keyboard-service-program-for-mac-notebooks|look into this|new_window=true]. As long as it has been less than 4 years from the date of original purchase you should be able to get free keycap replacement at the least. But more likely a replacement for the entire keyboard assembly.