SUs are the subject of a great deal of mythology, and the people who are telling you to retune for winter are passing some of that on to you.

There is a basis for that idea, however. The mixture carbs produce varies with air density -- denser air leans the mixture. All else being equal, cold air is denser than warm air. This does not mean that the air taken in by the carbs after the car has warmed up is significantly colder in winter, as it's coming from inside the warm engine bay and is heated going through the radiator. The engine itself does not want a richer mix in cold weather; you're only dealing with the carbs' ability to maintain roughly the same mix year-round.

I wouldn't change anything unless you start having problems. It's necessary to use the choke with properly tuned SUs for cold starts in any sort of weather, and the chokes should get you going in winter as well. You might need to warm up just a bit longer before setting out.