Right. I have done it.
You need two sizes of Torx screwdriver, the bigger one for the 3 screws in a line you that can see in the "door card" (DC) under where you put your have to pull the door shut, and the smaller one for everything else. You need a proper "screwdriver" type thing for the smaller ones, not the interchangeable bit things which haven't the necessary reach.
Work somewhere that you can fully open the door.
Remove the rubber cover that sits over the adjuster knob, the base of it is like a grommet that holds into the top of the plastic DC, you can do this with your fingers, no tool needed. Loosen the screw that holds in the adjuster knob, there's a hole in the DC just under the adjuster knob that you can put a screwdriver through, visible when you open the door. Don't unscrew it completely. Wiggle and push the whole knob assembly down through the door card.
Remove the DC. The Scudo manual on DVD is quite good (Bodywork part 1 page 1) - pull off the window winder, lever off the loudspeaker grille carefully with a small screwdriver, from the top. Remove the obvious screws you can see at the "corners" of the DC, and the one in a deep recess by the loudspeaker. Remove the loudspeaker (4 screws), and the screw holding the DC in a deep recess un the DC under it. Don't let the loudspeaker dangle, support it. Remove the three "bigger" screws from under the part where you put your hand to shut the door. There are some plastic "poppers" holding the DC to the door at the bottom/front, near the loudspeaker. If you prise off the DC these should "unpop". Finish freeing the mirror adjuster knob if you need to, and lift up/away the DC.
There's some foamed polythene film under the DC, glued to the door. You don't need to remove this.
Where the control cable goes into the door on the inside, it passes through a rubber grommet. Prise this out.
Unscrew the mirror - 3 screws on the inside of the door/window frame.
The mirror may come away - it may be not, if the adjuster cable is pinched between a white plastic thing in the door and the inside metal "skin" of the door. You can see this from the outside of the door looking in and down. If the cable is pinched, push it downwards with a screwdriver put on the cable by the white thing until it's not pinched, and push out the cable from the adjuster knob end and pull it gently from the mirror end (not hard or it will just get trapped again) and the mirror will be off.
Get a bit of stiffish wire, about the thickness of single-core mains cable. Make a 1/2" or 15mm curved hook at one end.
Feed the knob of the new control cable into the door (make sure the rubber mirror sealing gasket is on the mirror mount!), but not too far. The end of the knob should be catchable with your wire hook from the inside, through the hole you took the grommet out of. If you feed in too much control cable, you'll catch that in the middle with your hook, and not the knob, and you won't be able to pull the knob in the right direction. Catch the hook, and gently feed in a tiny bit more of the control cable while you hook in the knob and pull it in through the hole where the grommet was. Observation: It must be quite difficult, sometimes, being a gynaecologist.
Attach the mirror loosely with a screw, to stop it dangling.
Slip the grommet over the cable, and re-seat it in the door.
Push the knob into the DC, there's a flat on the side of the plastic that engages in the DC. Make sure it goes fully home, and do up the securing screw until it bites into the knob and holds it securely.
Replace the DC, replace all the screws in the DC loosely before tigntening them all. Replace the speaker. You did remember to put in that grommet, didn't you? Ah.
Screw the loudspeaker in again. The wires go at the bottom.
Re-fit the speaker grille and the door winder.
Screw in the three screws which hold the mirror on.
Job done.
