Programs can review new materials relatively easily.
@mcl -- there's a tool right on your dashboard to do this. It's called "Application Activity", you just set the start and stop dates/times that you want to see application updates for. There's a collapsed window just below it that you need to expand first, and then click the "Update" button, and it will show you all of the new activity. You can also limit it to the filter you are running. I personally don't find it all that helpful.
Realistically, the amount of material that pours in is insane. And what change/updates are we talking about that might actually make a difference? Usually it would be 1) a new Step score; or 2) a 4th LOR; or 3) ECFMG certification. Although you might ask your school to re-upload a transcript, one more grade on a 4th year rotation isn't going to make any difference. You can't update your application with new publications (at least, I don't think you can).
For Step scores, if it's going to make the difference between an interview or not, I've labeled those apps in ERAS so that I can quickly check if a new step score has come in.
It's very unlikely that a 4th letter will change an interview decision. Any 4th letter will be reviewed when you interview.
If ECFMG certification, we can easily search for that. If a program only considers applicants who have full ECFMG certification, once your file is updated they will see it to review. If they consider applicants who will obtain ECFMG certification before July, then whether or not you have it doesn't matter much.
The bottom line is that, other than a Step score, there isn't much you can add to your application that will make a difference. And for programs that want that missing Step score, they will likely have a way of finding it when it arrives.