That's where the skills of the decent retrofitters come in. There was one case of a DIY
Ateca mechanic lass that had bought all the parts for the motorised tailgate and vitual pedal but needed the mothership programmer. Dealers couldn't do the
coding since based on her Vin the
coding wasn't on the menu so they couldn't do it. Retrofitters in the South of England couldn't do it. At the time a German company sold the parts, how they remotely coded it, who knows, probably you had to go in. I'm told by East Yorkshire Retrofit that they can now do it. She probably ordered the parts from Germany.
Lesson here, not to assume that you can cut corners with a car order and get stuff post fitted later. You have to research the subject. Not all retrofitters are equal. Many people obviously enjoy customising their cars, the wrinkles of getting stuff fitted. Not all tasks are DIY due to the control mechanism put in place, the car's software. You have to pay attention at purchase to what you are buying, for lease and PCP cars their options to fiddle with things is limited since it isn't their car so they have a life of "detailing it" conversations of which polish to use etc. The secondhand market and real owners of the car can embark on post fitting things although PCPers strip out items when passing it back like the spare wheel, boot cover etc. I prefer to splash the cash and buy all the luxury items at the start.... and with Seat savings those for the Cupra now, my complaint is I'd have to buy Cupra bling now as well
. You can't win them all.