This is what Stevens does every season to start the season. He experiments with different combinations in various situations for the first month or so, and collects enough samples sizes of data to determine which lineups to go with in the long term. That's why his Celtics teams usually start off mediocre and then hit their stride by Xmas.
This team absolutely cannot afford a slow start. This team is too young and inexperienced to pull themselves out of a huge hole. They need continuity and familiarity with each other. I never know who is going to play from one game to the next, and for how long. If it frustrates me as a fan, i'm sure it frustrates the players even more.
It's too bad Stevens doesn't have any way of communicating that kind of thing with the players. The fact the players have only as much info as us is a real weak point of the NBA

And why, exactly, can this team mot afford a slow start? Do we have championship aspirations that somehow will only work if we are the #1 seed? I'd much rather see Brad tinker with lineups now (even if it costs us a couple of wins) than be screwed if a rotation player goes down because their replacement hasn't played any time with the rest of the rotation.
I honestly don't get why people get so worried about our rotations in October. This team will have tight rotations, and will know what lineups and combos work/don't work come the playoffs. If your main concern is how many games we win in the first couple of months, or how much you can predict what the rotation will be in any particular early season game, then I don't know what to tell you.