<p>My common app essay perfectly answers their optional essay. Would they allow me to switch?</p>
<p>What do you mean? You want your common app essay to be your supplement essay? You know they read both, I don’t think they’ll enjoy reading the same essay twice. </p>
<p>If you mean using the ideas from your common app essay, then yeah you can do whatever you want. But the deadline is already past. You could try and call them to see if you can switch.</p>