I fitted it in my face lift and had a little extra wiring to do. I do believe the pre facelift is plug and play because the wiring harness was fitted to accommodate everything.
No it was quite straightforward. I had to run a wire from the rear of the light switch to the DME. All instructions were provided as it was an official retrofit.
Only the early cars (pre Oct 04, I think) had the full loom in place. All facelift cars will need wiring. It relatively simple and you don’t have to splice into any existing wires. I think @srhutch is still making up cruise control looms at a very reasonable price.