Originally Posted by CrosswindSolo

Yes, after you submit you are given a link and code to log back into your application at any point to make any changes or updates. However, I had 3 LoRs on my app, one being internal, and before I could add the other 2-3 internals I was being sent, my app went into review and can't add them now. Hopefully at that point it doesn't matter, just a heads up.