Tommy Hearns got the draw against Leonard, which most thought he deserved to win, by training his legs to improve his punch resistance. It was the Sugar man who twice tasted the canvas. Foreman learned to relax and had very good stamina in his second incarnation. Lewis learned to use his size.
Victor Galindez changed from a pressure fighter to a retreating guy that would counter. And he was as good as anyone in the sport back then fighting off the ropes which is another thing fighters usually do not adapt well to try doing.
Joey Giardello turned pro with basically no amauter background and won a lot of early fights on volume punching and toughness. Once he stepped up in competition he was dropping decisions to good but not great fighters because he was getting hit to much. He really developed into a phenomenal boxer and a very sound defensively fighter that used movement to his advantage. A lot of his early fights are not on film but lucky for us we can watch his later fights and see what a complete fighter he turned into.
Bob Baker started his pro heavyweight career by bowling his opponents over. Writers of the early 50s were actually comparing his power to that of Joe Louis. However, bad hands soon put an end to all that. But he made up for the lack of snap by becoming a damn good combination puncher. That, with his natural heft got him to top contender by the mid 50s.
Mathew Saad Muhummad started his career as a boxer than more of a puncher and was so distraught after split dec loss to Eddie Mustafa Muhuammad that he changed his style and started slugging to take his destiny out of the judges and was a start of a unforgettable run.
I always thought Virgil Hill was a great example- no righthand whatsoever but a great jab and movement. so he always fought within his limitations and never tried to be something he wasnt.