I applied Single Choice Early Action to Princeton November 1, and I find out the admissions decision December 15. I hade decided that Pomona College is my number one choice, but since they didn’t have Early Action, I decided to do Regular decision. Recently, after returning from their Fall Weekend, I have decided I want to do Early Decision. Would it be possible for me to apply Early Decision 2 to Pomona (deadline Jan 1, admissions decision Feb 15), even though I applied SCEA to Princeton?
Yes, you can do that. I applied ED to Brown, and if I get rejected, I will be applying ED2 to Pomona.
@ap012199 thank you so much for your quick response! 
If you get in to Princeton, you will not be able to apply to Pomona ED I believe. SCEA is similar to Georgetown’s EA program, where you can apply to as many schools as you like but no binding agreements.
If you do not get into Princeton then you can apply to Pomona ED.
My understanding of single choice early action is same as above. You cannot have a pending ED application at any time before the SCEA decision is released. Also, if you are accepted SCEA, you cannot thereafter apply ED. If you receive an SCEA decision other than admission, then you can apply ED to another college.
Princeton’s SCEA rules: https://admission.princeton.edu/applyingforadmission/single-choice-early-action
There is no mention of any exception for later-deadline early decision (ED2) at other private schools.
Thank you all for your feedback. So if I was deferred from Princeton, could I then apply ED to Pomona? Is it only acceptance that will prevent me from applying ED, or is it acceptance/deferred?
Interesting question - ask your college counselor to call and inquire.
Since the Princeton SCEA admissions decisions are by definition not binding and are concluded by mid-December, my guess would be that you are morally able to apply ED2. Just my $.02.
Have you considered calling Princeton and asking them to change your application from SCEA to regular decision? That would clearly free you up to apply ED2 to Pomona.
I believe that Princeton’s SCEA program will only let you apply to other schools RD.
Both Harvard and Yale’s SCEA are a bit more flexible in that they allow EDII submissions as long at the notification date is after Jan. 1st:
Harvard: :After students receive notification from Harvard’s Early Action program in mid-December, they are free to apply to any institution under any plan, including binding programs such as Early Decision II."
Yale: “You may apply to another college’s Early Decision II program, but only if the notification of admission occurs after January 1. If you are admitted through another college’s Early Decision II binding program, you must withdraw your application from Yale.”
It seems that for Princeton, you can only to RD or non-binding rolling admissions to non-publics.
I would wait for your admission decision and then call Princeton and clarify the rules if there is any doubt. And if Pomona is truly your top choice you can consider if you can move Princeton to RD.
If you are deferred, then any obligation you would have had to Princeton has ended and you can make whatever future decisions you choose.
If Pomona accepts you ED, then you must withdraw your application to Princeton and everywhere else.
If Pomona is your first choice, why didn’t you apply to Pomona EDI? Princeton sounds like your first choice,
You can apply ED2 elsewhere, such as Pomona, after receiving a deferral decison on SCEA. The agreement you had not to apply early elsewhere officially ends upon deferral or rejection. A deferral is in fact an EA rejection. What has occurred with a deferral is that you are now considered only as a regular admission applicant, and as a regular admisison applicant you have absolutely no obligation to avoid applying ED elsewhere.
Once you are deferred you are in the RD pool. SCEA no longer applies.