How difficult is it to switch into Elliot?

<p>I got into GW EDI in the Columbian College of Arts and Sciences. However, my plan has always been to do a double major in both CCAS and Elliot. Because I couldn't apply to both schools at once, I applied to CCAS only. How hard would it be for me to get into Elliot after already being accepted to the school? Is it even possible? When exactly would I "apply?"</p>