Yep, all the mods functioned IMmEDIATELY.
I have enriched my car with all possible options (the car had a sunroof only), such as: power windows, power seats, power rear sun shade, heated seats, illuminated vanity mirrors, self dimming rear mirror, electric folding side mirrors, front door entrance lights, AMG bumper lights, third brake light, model "98 trunk lid lock and last (but not least) the full automatic climate control (the car had a heater only).
It was a bit difficult to get the climate control of a petrol car into my diesel (the airco pump and hoses/pipes had to be changed to fit), but everything worked at once which caught me by surprise (to be honest).
So, whatever the dealer says: they do not always tell the truth (the last sentence is to be read: they do not always know what they are talking about.
with a minor 600+k