Does this lengthen or shorten the life of tennis strings?

If you hit with lots of spin, especially topspin, this is going to happen. Moving the strings around will not help you much. There are two things you can do to delay breakage. 1. Buy a set of String-a-lings if they still sell them. They prevent string movement, and I used them a number of years ago. 2. Buy tougher strings. Otherwise, plan to get a lot of restringing done.