Had my xenons removed at first but due to a personal connection, they were put back not much later after compliance. Of course, the people who re-installed the lights never actually "insalled" them.
Usually, depending on the place, they will have one set of halogen lights for fitting (before compliance) and then all the other xenons there to sell as extras when the car goes... that way, the guys get more money, and not waste the xenons!
There is only ever one conversion done... the one that gets swapped around from car to car! Given the option, I think most people would pay 1K for the upgrade - luckily mine were free