That is a good question
@TruthSeeker . I think I may be thinking of 'core' differently from you. As you said:
? Does a liar, whose always lied, always have to be a liar-if that's at the core of the person?
You see, I see lying as a behaviour, or a response, not a core belief or trait. A belief may be (from history): it's the only way to keep safe. Or, honesty will be used against me. Or honesty is not something the person values. A core trait may be, inability to think clearly under stress, and a question may be stressful. Or a core characteristic may be extroversion, and grandiose lies add 'spice' or interest, in someone's mind. Or, the core trait may be an inability to have a conscience. Or little regard for other's feeling (a lack of empathy, which however can be learned). The possibilities are endless, as are the beliefs.
. Why can't you change your perception....and ultimately change the core beliefs in the person you are?
I think a person potentially can, but it would not be easy, and there would have to be reason to change. There would have to be sufficient desire or doubt, to begin to contradict it. And as humans we have a confirmation bias for what we already think is true.
They say every person has about 5-11 core values, 5-7 being the real strongest or most predominant, and to go against those threatens anyone's sense of identity, even if that sense is a less than ideal one.
So for example, if I am loyal as a Top 5 core trait, it is possible (but unlikely) I will become disloyal without experiencing great distress. However, I could become loyal to someone or somthing else, instead of seeing something as a betrayal.
ETA, I can not speak for anyone else, just myself, and of what I know or others have told me. Perhaps it was personality before much else? But for example, I will never become an extrovert, but I appear socially extroverted because I find people interesting, or life moment by moment boring without it. I was a peacemaker, or hated conflict between others when I was only 1 or 2 years old. I will never get upon a stage, or sing, but I've never been able to stop my body from dancing (as a child also). Etc Now those are just characteristics, but I'm not going to 'be' someone else. I like to love, I like to stay out of attention, I like to feel grounded and safe, I like to laugh, and I hate to fight and condemn. It hasn't changed yet, I don't think it will. Except to just give up on life, in totality. But in all those ways and more, it's (also) going to effect what I think about relationships, and how I show up in them. Being an introvert, I'might look very sociable, but I'm going to trust virtually no one. Especially when it comes to my most innermost thoughts or what is dear to me, or my heart. That, I think, will never change for me.