I’m applying both EA and RA. When time comes to submit the EA apps, could the application be changed for the RA time (like a new essay or adding new scores)?
I’m assuming you mean RD. Yes you can update the info.
You can update the info for schools you haven’t sent the common app to yet. But you can’t update what was already sent. Usually you do that by emailing the new info to the admissions office and asking them to include it with the application you already sent. New SAT or ACT scores have to be sent directly from the testing services, of course.