Obviously Muhammad ali, and Lennox Lewis who change his style during the Vitali fight, when Klitschko was beating him up on the outside, he roared in and beat the crap out of his opponent and finally stopped him.
Evander Holyfield. He was easily one of the best at taking any style or strategy an opponent could bring and then adapting to be competitive and even win the fight. At his best, he was phenomenal at doing it. Many of his opponents on the "best they faced" mentioned him. Tunney is another example.
Dammit George, you beat me to it. Marquez could do it all. The way he regrouped after that first round was just extraordinary. Marquez was always composed and thinking. Archie Moore is another cerebral guy that comes to mind that could remain cool under fire. He survived a similar situation as Marquez only he won via KO. I thought Marquez should have won that first fight hands down.
Maybe I'm mistaken but as great as Ali was, he was never really able to adjust to Ken Norton. Ali had great skill, speed, heart, an iron , and chin, but when it came to those Norton fights he had a ton of trouble. I only had him winning the second fight, and that was because he pulled it off in the final round.
Alexis Arguello did make the necessary adjustments against Ray Boom Boom Mancini on Oct 3 1981, and Salvador Sanchez against Pat Cowdell on Dec 12 1981.
And vs Ganigan. The knockdown really hurt his pride. He came up firing and blasting to the body for the next 2 rounds. You can see in his eyes how embarrassed he was.