Well unlucky for you, you cant change sam turret and sentry anymore. Personally, i think if you give the option to choose killstreaks for each class it takes a strategic element out of the game and kind of unbalances the game. Part of working as a team is deciding who has which k/s' to help the team win the game, if everyone could choose different k/s' mid-game i dont see how it can make the experience any better imo, i think it would be worse. And if you want this feature so you dont have to change your k/s' between games, then that is just pure laziness, it takes seconds to change it.