How does Jimmy Valentine change throughout the story "A Retrieved Reformation"?

Jimmy Valentine is a hardened criminal who immediately returns to safecracking when he is released from prison; however, after he unexpectedly falls in love, Jimmy changes his behavior and attitudes and becomes an honest businessman. But, later he must return to his former self, although it is only briefly.
As the story begins, Jimmy Valentine is handed his pardon by the warden, who urges him to

"[B]race up, and make a man of yourself...Stop cracking safes, and live straight."

Jimmy rejects this advice with a bold-faced lie: "Me?....Why, I never cracked a safe in my life."
Then, as soon as he walks out of the prison, Jimmy takes a train to a small town near the state line. There he makes contact with an old friend, who has helped to procure Jimmy's pardon from the governor. After a brief conversation, Jimmy asks him for the key to his old room. Opening his room, where the detective's collar-button yet lies on the floor from the day on which he was arrested, Jimmy pulls from its hiding spot his suitcase containing the tools he has used to break into safes. With this case in hand, Jimmy is back in business.
But, one afternoon as Jimmy climbs out of the mail-hack in Elmore, Arkansas, something happens to the safe-cracker: He falls instantly in love with a beautiful young lady who comes out of the local bank. Later, when he learns that she is Annabel Adams, the daughter of the owner of the bank, Jimmy undergoes a change of heart about robbing this bank. For, he registers at the local hotel, telling the clerk that he is seeking a location to start a new business. When the clerk answers Jimmy's inquiries about the opportunities for opening a shoe store, the clerk informs him that there are no exclusive shoe-stores in town.So, it is Ralph Spencer, "the phoenix that arose from Jimmy Valentine's ashes" that emerges from the hotel. He introduces himself to pretty Miss Annabel Adams and they grow to love each other so much that Ralph proposes marriage. Jimmy Valentine is reformed. And, since he no longer needs his tools, he decides to give his "kit of tools" to an associate from his past. On the day that he carries his suitcase from his old trade to travel to Little Rock and deliver them to his friend, detective Ben Price surreptitiously waits for him at the Elmore Bank, having traced Jimmy Valentine's whereabouts.
Instead of being able to depart early, Ralph Spencer is drawn into joining the family at the bank because this is the day that Mr. Adams wishes to show off his new safe and vault. Still, he has Dolph Gibson waiting for him with his horse and buggy so that Ralph can go to the railroad station afterwards. But, unfortunately for Ralph, Annabel's niece locks herself into the vault. Since this vault is set by a timed mechanism, no one can get this vault open. If they wait until it is mechanically released, little Agatha will suffocate. When Annabel turns to Ralph and asks, "Can't you do something Ralph--try, won't you?" the irony of this question is profound.

He looked at her with a queer, soft smile on his lips and in his keen eyes."Annabel," he said, "give me that rose you are wearing, will you?"

After he places the rose into his pocket, "Ralph D. Spencer passed from away and Jimmy Valentine took his place."
Pulling out his tools from the suitcase, Jimmy sets to work with his drill. In a quick ten minutes, Valentine opens the safe and Agatha emerges unscathed. Replacing his coat, Jimmy Valentine heads to the front door of the bank. However, he is accosted by Ben Price, the detective who has traced him to Elmore. With resignation, Jimmy says,

"Hello, Ben!...Got around at last, have you? Well, let's go. I don't know that it makes much difference, now." 
"Guess you're mistaken, Mr. Spencer," he said. "Don't believe I recognize you. Your buggy's waiting for you, ain't it?"

It is, indeed, a "retrieved reformation" that Jimmy/Ralph receives.