Now that is an interesting question - since no one breaks in bike tires.
I did fall flat on my face because I took a sharp turn on sealed asphalt before I wore the tire release compound off. It rather shocked me to have the tire give out like that. But, other than scuffing up a tire tread, there isn't much to breaking in a tire.
But, as with any race preparation. Don't change anything the night before the race - if/when you do change something, go on a nice moderate ride just to make sure everything is playing well together seated, tightened, fluid, etc.