Yes there is. Keyboards with function keys are only used to switch to F10. The addition of F11 and F12 as a standard occurred some time in the late 80s or early 90s, from memory. Changing the enumeration for existing scan codes 69 and 70 will violate compatibility with older keyboards. Remember that before USB (or PS / 2, for that matter) the keyboard had a short 5-pin DIN connector, and you could not say what was on the other end.