From what I understand they can basically drop in along with required wiring harness and the controls then be coded with VCDS to let the car know that option is installed.
If you're going to the trouble of putting in a new climate contol interface, look at getting the Mk7 one instead of the stock one. It provides a more modern look which is nice. I can't find my photos of that at the moment, but if I find them I'll post them back here for you.
There is some info here: Climate control conversion
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