According to the scriptures, some results can't be changed. Even the Buddha became injured. He became sick a few times. This is because of his past Kamma. Even as the Buddha, the most wonderful, loving person ever, even as that person, he still had to experience some of the results of his past negative Kamma. So it's more of a Right View to believe, as far the teachings go, that some results can't be changed.
Now, in a sense the results can't be changed, but our reactions to the results can be changed. An example I like to give is that of a glass of water. Say you have a glass of nice, clean water, and you put two big tablespoons of salt in it, stir it up, Do you want to drink it? It's not going to be very easy to drink at all. Two tablespoons in one glass of water. OK. Now, think of a bathtub full of nice drinking water. You take the same two tablespoons of salt, put in the bathtub, stir it up. Can you drink that water? Yeah, easy, you won't even taste the salt because while the amount of salt is exactly the same, the amount of water is vastly different.
In this example, the salt represents our past negative Kamma coming to fruit. The Dukkha, the bad stuff coming to fruit. We can't always prevent it from fruiting. The water represents our good Kamma. If we've done heaps and heaps and heaps of good Kamma, this salt is not going to taste so bad. If we've done only a little bit of good Kamma, and we get that salt, it's going to taste bad. So, if you want to prepare for the possibility of your past Kamma fruiting, make lots and lots and lots of good Kamma, and then you will be more ready for it.