How often do boxers switch styles/approaches?

... Other thoughts or examples of how or why this happens? ... Andre Ward represents a good example...

I'm talking about the way Cotto went from aggressive bull to dancer/boxer and now fights like a hybrid of the two. Pacquaio went from whirling dervish to cautious and calculated boxer/puncher. Mayweather went from mongoose style boxing of precise combinations and skillful evasive defense to calculated one and done counter-puncher with clinch defense. Other thoughts or examples of how or why this happens? If you're moving up in weight+ fighting better oppsition+ getting older, u have to change up ur style, when you're carrying a lot of extra weight u can't throw the same number of punches like u used to do at the lower weight, ur stamina won't hold out, the same goes when u r getting older, plus when u get older ur reaction time is slower so u need to avoid the exchanges as much as u can and fight from the outside more. Also when you've been fighting at the top too long and everyone knows how u fight, one day someone will figure out how to beat u just by watching u and therefore u have to change up and be able to adjust, u can't keep doing the same things over and over again, when u overuse a move at this level u will pay for it against high level of opposition, Floyd for example overused the pull counter against Maidana and as a result Maidana times it and countered Floyd counter by a beautiful right hand, Mayweather knew Pacquiao best way to get in on his opponent which is to lead with the left to the stomach then come up with the right hook then the left hand all while moving forward, so whenever Floyd felt Pacquiao was trying to go down stairs with the left he stood his ground and fired a sharp right counter which nullified Pacquiao's offense cuz it was sharp and hard for a counter punch that fast, and so on. This is a result of Pacquiao being on the scene soo long that his opponents already know how he operates. Floyd is a unique fighter cuz of his versatility, he finds that secret weapon every fight, against Judah for example Judah was countering his jab, so he didn't wanna play that jab counter game with Judah who's pretty fast too, so what he did is to throw his jab then bend at the waist to avoid the counter, this sounds simple but believe me bending at the waist is the adjustment Floyd made to win the fight. Fighter that rely on speed, power and volume punching don't last cuz once the speed and the stamina are gone they have nothing to fall back on, but with Floyd he's a thinking fighter, so even at the age of 38 where he's slower and with less power due to accumlation of injuries, he's still the best fighter in the world, same with Bhop and so on.