I don’t know about the A3, but if it’s anything like my previous A4, it’s a no go, as the windows would need to come out. Plus paint doesn’t stick to chrome so quite abit of people would be needed. Wrapping is a better option, but I couldn’t find any wrappers who would do mine as it was ‘more effort than cost’ they all said.
I had my chrome trim on my A3 saloon wrapped with gloss black vinyl. Think it was about £100, had a go myself first but kept getting bits of dirt stuck underneath it as a didn’t have a clean wind free place to do it. Hence a paid someone else to do it. Took them just over an hour.
I have seen a video on youtube where they did all the chrome by painting - I too wondered about getting paint to stick to chrome, but satisfied myself eventually that it probably is not actually chrome and what we are actually looking at is some sort of Audi alchemy on aluminum or paint finish!!!
When they took the trims off it looked fiddly but possible, much like taking any trim to bits, Audi design it to be put together quickly on the line and worry about getting it to bits afterwards!!!!