I always change my mind about everything, and I never change my mind about anything.
That flexibility is intrinsic to being human — more, to being conscious. We are (or should be) constantly learning new things, absorbing new information, and reacting to new ideas, so of course we are changing our minds. In the most trivial sense, learning and memory involve a constant remodeling of the fine details of the brain, and the only time the circuitry will stop changing is when we're dead. And in a more profound sense, our major ideas change over time: my 5-year-old self, my 15-year-old self, and my 25-year-old self were very different people with different priorities and different understandings of the world around them than my current 50-year-old self. This is simply in the nature of our existence.
In the context of pursuing science, however, there is a substantive context in which we do not change our minds: we have a commitment to following the evidence wherever it leads. We have a kind of overriding metaphysic that says that we should set out to find data that will change our minds about a subject — every good research program has as its goal the execution of observations and experiments that will challenge our assumptions — and about that all-important foundation of the scientific enterprise I have never changed my mind, nor can I, without abandoning science altogether.
In my own personal intellectual history, I began my academic career with a focus on neuroscience; I shifted to developmental neurobiology; I later got caught up in developmental biology as a whole; I am now most interested in the confluence of evolution and development. Have I ever changed my mind? I don't think that I have, in any significant way — I have instead applied a consistent attitude towards a series of problems.
If I embark on a voyage of exploration, and I set as my goals the willingness to follow any lead, to pursue any interesting observation, to overcome any difficulties, and I end up in some unpredicted, exotic locale that might be very different from my predictions prior to setting out, have I changed my destination in any way? I would say not; thesine qua non of science is not the conclusions we reach but the process we use to arrive at them, and that is the unchanging pole star by which we navigate.