S90, isn't that thing late model enough that the headliner just slides back independent of the sunroof and then you just shoot the four screws that retain the sunroof loose and remove the panel, thus allowing you access to the selector gates?

Does it have a glass sunroof panel or is it still metal?

In looking at Vadis is shows that if you have a glass panel one then it is as I outlined above. If it is still a metal lid then it will be the old school stuff.

1. Put the sunroof into vent position.
2. Reach into the open vent position from outside the car and push the sunroof headliner down enough that you can get your hand inside and undo the spring loaded clip that attaches to the head liner.
3. With it dettached go back inside and slide the headliner back towards the rear of the car. This part can be a little tricky as it is still held in by a couple of clips up front and it can be a pain getting it loose there and making it slide correctly in back.
4. Now drop it down from vent and remove the 6 screws that retain the lid, pull the lid out of the hole and change out your selector gates.

Good luck,
Mark