<p>Without commenting on the OP’s motives, I think the answer is self-evident: of course you need to withdraw all other college applications immediately if you’re admitted ED, because that’s what you promised to do when you signed the ED Agreement.</p>
<p>The language of that agreement couldn’t be plainer:</p>
<p>
</p>
<p>When you sign the Early Decision Agreement, you are attesting that you have read and understand your responsibilities under the agreement, and consenting that your ED institution may share the nature of the agreement and your ED status with other schools. Your GC must also sign, attesting that s/he has advised you to abide by your ED commitment. It’s a done deal. If you violate the agreement, there could be serious consequences:</p>
<ol>
<li><p>Your ED offer could be withdrawn.</p></li>
<li><p>Your ED school could notify other schools to which you have applied, and they could deny you admission or rescind offers already made on grounds that you violated your ED agreement with another school.</p></li>
<li><p>Your HS and your GC could be in hot water with your ED school, creating problems for other applicants from your HS in the present and/or future years.</p></li>
<li><p>Your GC would be fully entitled to conclude you are a dishonorable person who reneges on solemn promises, and so state in supplemental information supplied to colleges to which you are currently applying or to which you may apply in the future, as well as to prospective employers, FBI agents doing background checks for federal jobs requiring security clearances, and so on. </p></li>
<li><p>You absolutely are harming other applicants to your non-ED schools. Every school has a target number of admits, based on its expected yield and the target size of its freshman class. If you break your ED agreement and do not withdraw from, and are subsequently accepted at, a school you have no intention of attending, you are taking up a spot on that school’s “admit” list and denying that spot to another applicant who gets bumped to the waitlist. As we all know, being waitlisted is not the same as being admitted; at most selective schools, one’s chances of being admitted from the waitlist are almost vanishingly small. That applicant’s options look very different at that point, and s/he may very well accept another offer of admission at a third school, in turn potentially denying a spot there to yet another applicant, and so on. Lives are changed, all for no good reason.</p></li>
</ol>
<p>Beyond the potential consequences, there’s an even better reason to honor your ED Agreement: it’s the only right and honorable thing to do. This is not a silly game; it’s a serious commitment that you presumably made in good faith and conscious as to its implications. If you didn’t really intend to honor that commitment, you should not have made it. If you didn’t understand what you were agreeing to at the time, you also obviously shouldn’t have agreed to it (and you effectively misrepresented yourself in signing a form saying you had read and understood the agreement). In either case, you should immediately withdraw your ED application, or ask that it be converted to RD; otherwise, you are applying ED under false pretenses, and that is not an honorable thing to do.</p>