Chosen Solution
If I were to use a keycap from an original, genuine MacBook Pro keyboard, would they fit on an ifixit replacement keyboard? Specifically, I have a late 2012 Macbook Pro and I’m purchasing this keyboard, MacBook Pro 13" Retina (Late 2012-Early 2013) Keyboard
Replacing the keycaps is not something I recommend as they are tricky! More often than not people damage them in the process of taking them off or putting them on. Apple gets keyboards from a few different suppliers, so unless you know which one yours is you could just end up with a mess! Apple 13” Retina Key Caps