You should rotate your tires more often.
Practically no. By the time the studs are worn out, tires are too worn for you to install new studs and even if you could, the cost of replacing them would be more than the tires are worth.
Winter tires should be changed out when the tread has been worn down to around 1.5mm to 1.6mm in thickness, after they have been worn down more they are considered worn out. To measure the tread of ones tires one should use a tire gauge which can be bought at websites such as amazon.
If you are wondering how you can repair your worn out auto tires because your tires went flat, then you should check out Repair Your Own Tires Guide. It is online and free.
You tires are worn out because either the car needs an alignment, you are running them with either too low or too high air pressure, suspension parts are worn, steering parts are worn, or the tires were defective.
Too much camber and the tires aren't aligned right so the tires get worn easily
Tires are changed during an auto race because the tires get worn down by the track. It is safer to have good tires than to have tires that are worn down that could blow apart and cause accidents.
they are rethreaded
No, If the car "pulls" it is because something in the suspension isn't inspect. Can be worn tires, bent suspension parts, or just worn suspension parts. If tires, rule out by swapping rears for front(if the tires are the same size). Can also look at the tires, If 1 of the tires have a side of the tire that is worn more than the other, that is the side with the problem. Some suspension damage can be seen by the naked eye. If it can't "usually", it can be fixed with an alignment.
worn out
If you're having to put air in your tires frequently then your tires probably need replacing. Also if the tread on the tires is worn down they should be replaced (a symptom of worn tread is the tires squealing on the road for no apparent reason).
Yes, the faster you go the more likely you will hydroplane, especially if the tires are worn.