Personally, I would simply enter the engineer code, and then remove the 12v and 0v wires on the 'bus' connection inside the main box.
This is easy to spot as its the only block that sits on its own, with 4 terminals, at the bottom of the circuit board.
Then remove the old keypad, noting which colours are
12v
0v
data
Clock
The new 9943 keypad has exactly the same connections, just in a slightly different place.
Once this is connected, simply reconnect the 12v and 0v at the panel, shut the cabinet, and return to the keypad.
You might have to press a key to make the display come back, but you should be able to press 0 9 9 then 'tick' and exit engineering mode.
To add fobs, simply add a new user in the normal way, but offer up the fob rather than entering a number.
Hope this helps!