I don't know about UNECOM, but if you have good reasons it's a possibility. You'll have to talk to the admissions office about this. Feeling that your not ready... I'm not sure how that is going to present you to them. They felt you were ready to give you the opportunity to go there, but I don't know if not being ready on your part is reason enough for them to let you defer until next year. Although if you have concrete reasons why you feel you're not ready (e.g. family issues, etc.) then you have a good chance at getting the deferral.