Can a person change? Loaded question, one with many answers. I have vacillated on this many times myself, but I think I have an answer now, and that answer is yes. The question is how. I think the most effective thing for me has been to just find a rule that makes concrete a particular principle you want to abide by and then stick to it. Simple as that. I think it's much more effective than big sweeping generalities, because it's quantifiable: Did I break my rule? Did I not break my rule? If you have to will to stick to the rules, then you can change. And I feel like simple rules can have profound effects.
Here's a little example from my own experiences. At some point, I saw one of Uri Alon's tips on how to give a good talk, which is that every slide must have a title that is a complete sentence–subject, verb, object. I found this transformative in putting together my talks, because now every slide has a point, one to the next. And it's just such a simple rule. At first, I found myself fighting this rule, because it was a big change. But now I can't even imagine preparing a talk any other way. It's the perfect example of a rule: quantifiable, actionable, consequential.
Lots of other rules, many of which are well known. Another rule I try to follow is to avoid the use of "you" language in my interactions, which is bad for communication (e.g. compare: "You are doing that wrong" to "I usually do that differently"). For a while, I thought, "Hmm, I can't think of how to say this without saying the word you". But I followed the rule and just kept my mouth shut, and afterwards I realized that I was honestly just better off not saying anything. It worked! Over time, it just becomes second nature. And that is real change.