Is it possible to replace the top case with the AZERTY keyboard of a 15" MB Pro late 2012 (usb 3.0) by the top case with QWERTY keyboard of a 15" MB Pro Mid-2010. Do they have exactly the same dimensions?
At one time it was possible to make the change and in the end it became impossible in the official Apple network. The only solution I could offer you is to buy and replace the keys. I had done it one 2011. ok it's long but I changed the keyboard for 5€... then just change the layout of the language in the keyboard preferences.
Whilst the topcase-and-keyboard is interchangable, changing the keyboard's nationality layout does not change what the machine knows as its native tongue. Yes, it is possible to change the keyboard layout in the OS to match the new languagr-layout, but that only takes effect once you have logged in - at the login screen, the keyboard will still be using the original language layout.