Are you in that peculiar situation of having an extra set of IR-remotes left
and a car coming without one? No problem;

Most CX's have this type of IR-remote

But also this mini-remote is available

The mini-remote is not as simple to decode but the standard remote use a
very simple encoder; the integrated circuit "TEA5500" from PHILIPS.

This is the datasheet of the circuit

TEA5500.pdf

The code is entered thru the pins 5 - 14 by either connecting to GND or Vcc
or to disconnect (floating).
From the factory this code key was entered by a simple drill-robot

As you can see in the above picture the same pattern is drilled into the receiver
as well with one great exception -> it is reversed! (The pattern that goes from
pin 5 to pin 14 on the sender goes from pin 14 to pin 5 on the receiver)

If you need to alter the code just bridge or cut the PCB at the corresponding
positions on either part. Please note (in the datasheet) that you may have to
disconnect a pin (let it "float").

I suspect that everyone that needs to do this operation will download and print
the datasheet anyway so there is no meaning to further explain the details.

Good luck!

PS About the code written on the little tiny paper in all units; I don't think it is
necessary to fully understand the code. Just copycat the drilling and you'll be of
anyway. If someone with lots of key lying around feels like it I'd welcome a
code chart of the corresponding code vs. drilling...