Not from the start of the game. Only from the one scenario, the one which starts early 1805. In the August 1805 you would be breaking with what had historically already happened.
I haven't look directly into the events, but it may be as simple as setting out one event, which puts Austria in the coalition. You could easily mod that yourself to prevent it from firing.
Of course, I would expect France to have even more reason to attack Austria. France didn't attack Austria because Austria joined the coalition, but because it was France's political goal to reduce Austria's influence on central European politics.
But IMHO (this is of course only conjecture, because we are talking about alternate history), Austria could only appease France, if France gained about the same results through the appeasement, as France gained historically through the war. That would be the appeasement, not that Austria didn't join the coalition. And that would mean that Austria signs the Peace of Pressburg in early 1805 without having fought a war first.