GT is my #1 right now so I would like to apply EA but I think my app will have more for the RD round. So can you change/add things to your app in the event of an EA deferral?
Yes, you can update your application, usually in the form of a letter explaining what you have done since the EA round, and by sending them new/improved test scores. Personally, I might wait for RD if that’s when you feel your application will be stronger (there is no advantage in applying EA, the acceptance rate is often lower EA than RD) but since it’s not restrictive EA it couldn’t hurt, unless you REA somewhere else (HYPS). Send your application when it is strongest - if that’s the RD round, send it then.