The reason I say that these were simply refinements to his existing style is that he suddenly didn't switch to being a more defensive boxer, or strictly a counterpuncher did he? He didn't start relying on winning on points and being a more conservative, decision winning fighter. Duran at lightweight still was a "ko the opponent" sort of guy...that didn't change..rather the enhancements made to his style...the tweaking, so to speak, simply made him more effective in dealing with the DeJesuses of the boxing world...and enabled him to stop that formidable opponent as well. Also, Duran was smart, and had, IMO, pretty much doped out DeJesus at that point, and the Puerto Rican, despite having obtained the WBC lightweight title, had seen better days by then as well...the loss to Cervantes having done him no good along the way. Duran thrived on aggressiveness and he simply retooled his existing style into being the hallmark of effective aggression....but he didn't really change his style.
Nigel Benn after he moved up to super middleweight became a more discerning puncher and racked up a series of steady points wins and only let it all hang out once more vs McLellan. Lennox Lewis became a cagier boxer under Steward but the memory of being flattened by McCall was possibly as much of a factor and he changed from being right hand happy to a patient jabber.
Many of the "lighter weight" fighters could change their styles as need be. One reason is they had all-around boxing skills, plus movement.
Matthew Saad Muhammad, while never great defensively, used to move and box for the most part - until losing a questionable split decision to Eddie Gregory (Mustafa Muhammad) in 1977. After that fight, he stood and traded punches much more. He tried to revert to his old style against Dwight Braxton, but by then he had lost some of his sharpness and reflexes.
