Prescreens are likely the first impression an auditor has, and if they replay them, may be a last impression as well. I agree with @pookiesunshine they are not to be taken lightly. And in the event of inclement weather (as occurred this year) they may be the only thing certain faculty “see” of you, if they don’t make the live audition.
I would also say, its probably NOT a good idea to change your look between prescreens and auditions. No going from blonde to black. Short bob to long curls. They need to “know” you and if you look different everytime they “see you” uploaded headshot/prescreen/audition/headshot they are going to get confused.