The normally closed contacts of the relay are wired in parallel with the 'park' switch of the mirrors. With the relay contacts open, the position will still be dictated by the position of the switch.
I'm not sure I understand this, as the mirrors on my current Initiale appear to work in exactly the same way as they did on my Privelege, except for the fact that they have the memory function (which doesn't appear to make any difference to the switch.)
I also remembered that the Pug actually tied the mirrors into the central locking rather than the ignition. Now that'd be an even neater trick. Can anyone work out a circuit to do that?
If your mirror has a memory, then it must have position feedback on the mirror location, and this is apparent in the Multiplexed wiring diagram. This uses the logic contained in the 29 pin block associated with the window motor. My understanding is that this is the local hub for the CAN bus, and thence drives the local actuators as if on a hard-wired car.
For the sake of the motor folding, it simplified things, as all that comes from the switch is a signal requesting "Fold" (rather than drive commands for "Fold" and "Deploy") and any time you duplicate that request, the mirrors will fold.
However, the request must be in place all the time you want the mirrors to remain folded, and the central locking (probably) only sends a "momentary" signal, which you would have to create some form of latching logic for.
Cannot immediately think of any signal that has this sort of logic, except perhaps the window control (which remains active until you shut the drivers door after removing the ignition).
Note that further down the French thread, there is the switch mod to isolate this relay, so the mirrors remain only under manual control for the multiplexed version. (The non-multiplexed bypass mod is in its original post)
But what is the problem with having the mirrors open only when the ignition is active? What alternative operation are you trying to achieve?