Not really, the whole "started to play defense" thing was super overblown to fit the narrative of Bowman being the best coach of all time and Yzerman being the consummate team player.
Yzerman played defense in the 80's he killed penalties, he was double shifted as the third line center, he backchecked, literally the only difference is he cheated a bit more in the 80's, which every star forward did(played on the offensive side of the puck instead of the defensive for anyone who has played hockey will know what i mean).
Only difference is in the 80's and early 90's he played in the division that was basically a bye for the smythe division on one of the worse teams in his own division.
Yeah, exactly.
Yzerman obviously got better in this regard in his 30s, but the notion that he was a complete one-dimensional creampuff during his big offensive years is total revisionist history to fit a narrative and completely incorrect.
From the age of 22-23 he was considered a quality two-way forward, killed penalties, and was receiving Selke votes. Published scouting reports from the late-80s without fail reference his responsible defensive game.
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Back to the original question, the best example I've ever seen of a guy completely changing his game/identity is Marty Reasoner.
When Reasoner was drafted and coming through the St. Louis system, he was considered a hugely talented, soft-as-butter skill center, and was often compared to Craig Janney, the poster boy for soft-as-butter skill centers. But when his career stalled in St. Louis and he was exiled to Edmonton, he completely remade himself into a gritty, defensive center who was a shot-blocking machine. And proceeded to have a very long career as a specialist defensive #4 center.
Wasn't really successful though
