Ah, see, I don't consider those as core beliefs, which makes it easier for me to see them as malleable, to see they can change for the better. I think those are negative imprints, not intrinsic, and that my core is purer and stronger. The rest just requires reeducation, both experiential and educational. DBT books can help with something like that, a program of affirmations too, as far as the mechanics, and lots of other tools in my experience. Reprogramming those deeply ingrained negative cognitions and thought patterns is definitely, absolutely possible, but as you've discovered, it does take a lot of time and work, like strengthening any muscle.