Turns out the retaining clip for the halogen bulbs prevents the fitment of LEDs.
Now i'm looking for a set of spare ones to modify them but can't find any. I prefer ordering them online and haven't asked a Citroen dealership yet.
Service shows no part number and eBay only offers me the wire type which i guess is used of the regular C3.
I haven't checked the high beam H1 clips yet but the low beam H7 clips are much like these:
https://www.amazon.co.uk/Sourcingmap-a1 ... B00BLZ9SEC
edit: I called the local Citroen garage and they told the clips are not sold separately. But according to them it is some kind of standard clip used on other cars too so i guess i'll just have to compare it to the other like the one in the link.