Yes you need to change your strategy thoughout a tournament to adjust for changing stack sizes and ICM. In the early phase of a tournament, ICM is still not important, so you basically play the same way, you play in a cash game. Your only focus is winning chips, and if risk taking result in you busting, then you just reenter or play another tournament. Just like you reload in a cash game, when you get felted. But as the bubble get closer, you need to start making adjustments. Both to make it into the money yourself and to take advantage of other players, who become risk averse, because they want to make it into the money. At the same time blinds also go up, and the strategy for playing a 20BB stack is different from the strategy for playing a 50BB stack or a 100BB stack.