Usually, in PSA land, usually the outside connector is the same regardless of the headlight type, all taking 12V in.
Might require changing some headlight parameters in BSI so that the car doesn't expect the presence of side-to-side turning bulbs (I think only HID bulbs turn, not necessarily halogen ones but not sure about DS5 though?)
However, I do wonder how the vertical aim could be made to work. Usually with halogen headlights there's manual aim control which I'm obviously missing. With HIDs there are level sensors. Both will ultimately drive the beam up and down but it might be too optimistic to venture if BSI could realize it still has the sensor readings to drive the halogen headlights up and down? It might work if there's a pair of wires for the vertical aim motor and BSI drives them but if BSI just sends the height info to the HID module which then internally drives the motor then that will never work.
I have switched between HIDs and halogens on my C5 but that model is easier because the whole car is self-leveling and there's no need for any vertical aim specifically
