Hi there,
Did it not to long back on my Leon (not really using it, did it only out of interest haha)
Basically what you would need is the back dome light (Part number 6Q0947291A) and some cables.
I removed the entire headliner which is the trickiest part (there are some good videos about it on
yt)
Remove all the sunvisors, front dome light, top door handle thingies, the inner mirror and work your way from the front to the back with all the trims on the side.
(Installing/removing the inner mirror is also a hard one, took me some time, but definetly doable)
On the other side of the headliner there are actually some markings where the dome light would be from stock.
I have cut a hole in the headliner which nearly fits the dome light, but did not turn out as bad as it could be.
My recommendation for the headliner removal/putting it back on:
Remove as much plastic trims as possible, it will save you a lot of headache
(A pillar, B billar trim, and so on)
The headliner is only hold by 2 clips in the trunk and by the plastic trims.