As much as I understand the law of Kamma within Buddhism, no, your death is coming at a certain point. This is just my understanding and I'm not sure it is true, but I believe you can't actually extend your life as death is such a big event in our life that it is predetermined by our Kamma.
As to affecting the length of our future lives, within Buddhism there is the belief that the more we do good actions, especially in regards to giving medicine and helping others with their health, that has the Kammic effect that gives you a longer and healthier life in the future.
Apparently during the Buddha's time it was not uncommon to live to 120, compared to today of 100. I think one monk lived to be 160. He had perfect health, never had a single day of sickness in his whole life or never got injured. He was the only person to have this kind of health, as even the Buddha got sick and injured, but this one monk supposedly lived 160 years and never was sick and injured. What was the reason according to the scriptures? He had been a doctor for 500 life times. According to Kamma, if you help other people with their health, you will then get longer and better health in your future.
Now even if the purification in the mind does not extend our life, or make us healthier, what it does do is give more inner calm and peacefulness despite being unhealthy or when we are dying. So if we do purify our mind and heart we are actually living life more fully, in the time that we have left.
For example in this retreat there were a few people who were sick, some are old students, one or two are new people, yet the old students were able to deal with their sickness much better. They can reflect on how fortunate they are to be here, the sickness is impermanent, their sickness is not so bad compared to other's sicknesses, all these different ways of thinking helped those people to actually live this retreat with a happier, more peaceful mind.
Some of the other people who are sick are more depressed, that is normal, because they don't have as many tools. So in that way, by purifying our mind we actually live our life more, healthier and happier.