After Tyson lost some quickness and reflexes, how could he have developed his game to better compete? (Yes, I know he wasn't motivated, but let's say he regained that motivation post prime. It's a hypothetical...could he have still beaten the best with a style adjustment?)
Don't keep loading up on punches with no setup. Tyson was out looking to wing bombs and get the fast knockout in the 90s and 2000s...the problem is that he would neglect setting up the punches and working smart. He would come rushing in with punches looking to force the explosive moments rather than exploding when the opportunity was there. Forcing the moments led to him gassing more and becoming easier to neutralize.
Not much he could do to be honest. He could have employed feints more, and been a bit more tactical in his footwork. A fighter with that style, and those physical limitations, is always going to have serious problems when his reflexes go.
This is basically the problem in a nutshell. Tyson still had his huge punch, but he started relying on it alone. His fight with Francois Botha is typical of the period. Botha was outboxing Tyson and frankly with relative ease. He was even showboating at one stage. Showboating with a prime version of Tyson would have been just plain stupid. Eventually Mike landed his handgrenade on Botha and crumbled him. But if he'd tried to set up his punches better and worked his way into a position to unload, it might have been much shorter.