Q: Should I have my racquets strung differently for play in hot weather? What about cold weather?
A: Some players—and many pros—do use different tensions based on the temperature and humidity. It's a bit less practical for amateur players since they usually don't have loads of spare racquets and professional stringers on call every time they take the court; however, if you have enough spare racquets (multiple racquets of the same model are best) you can certainly have a few of them strung up at varying tensions for use in different weather conditions.
In general, strings will play a little bit stiffer on cold days so it's not a bad idea to reduce your "warm weather" tension by 2-3 pounds if you're expecting to play in cold weather. Like most other string questions, it's important to keep in mind that every situation (and player) is a little different. A 2-3 pound reduction is a good place to start, but if it feels like too much—or too little—don't be afraid to experiment!