It is true that Hester Prynne's actions, as well as those of Arthur Dimmesdales's influenced a number of changes to take place in the novel The Scarlet Letter.
Unquestionably, the most significant change is Hester Prynne's own transformation, from a feeble woman, into a strong one. This is because Hester is the only one of the characters whose own story completes a full circle that goes from pain, to shame, then resignation, acceptance and, finally, closure.
Hester's time in prison made her a stronger woman. She took the scarlet letter, which was meant to be a symbol of humiliation and shame, and transformed it into a token of separation which, later on, is seen as a symbol of distinction. Hester goes as far as stating in Chapter VIII, "The Elf Child and the Minister", that the scarlet letter has actually made her into a better person
...this badge hath taught me,—it daily teaches me,—it is teaching me at this moment,—lessons whereof my child may be the wiser and better, albeit they can profit nothing to myself.
Not only does she try to make the best out of her sad situation, but Hester also keeps her innate talents at the needle quite vivid. So great is her talent, that the people of the village go to her to get fine and beautiful garments. Even more significant is the fact that Hester heals her pain and isolation by altruistically helping others; she becomes the embodiment of a true, Christian, woman during a time when anger, resentment, and self-loathing could have taken the best of her. Hester comes out as a woman who has grown beyond her difficulties and can survive any future ones.
Contrastingly, however, Dimmesdale- a man who once was the shining star of the village- changes negatively into a sickly, weakened, and ultimately failed man. He is the exact opposite of Hester. While she strengthens despite of ignonimity, Dimmesdale weakens right in front of the clamor of his fanatic crowd. To make matters worse, Dimmesdale enters and leaves the plot without having acquired any higher knowledge about himself, Hester, Pearl, or even the world around him. In fact, he may have ever missed the entire gist of his experience with Hester; in his eyes, he committed a sin with Hester and there is no other way around it but to punish himself, and submit to the Will of God. He does not even give Hester a second chance at love. Dimmedale's character is, in many repects, quite flat.
Similarly, Chillingworth does not suffer from any epiphany. His rage and thirst for revenge drives most of his role, leaving him with very little room to grow or transform. Like Dimmesdale, Chillingworth's small changes are negative. The only thing that surprises the reader is seeing how Chillingworth left his fortune to Pearl, even though she is not his daughter, but the daughter conceived by his wife and another man. Unfortunately, his actions may have been out of guilt, rather than out of a sudden change of heart. Very little suggests that Chillingworth ever puts his rage behind, even on his deathbed.
As far as Pearl, she just undergoes the typical changes of a young woman who has finally identified her father and now can move on with her life. She does so, and actually takes care of Hester, sending her money and settling her comfortably in the village. In a way, Pearl's own life comes also into a full circle.