Short answers:
Yes contact the rush chair of ABC and see about COBing or some other arrangements. If they remember you from last year that may expedite the process. But do it sooner rather than later.
Mention that you're planning on being a 5th year senior, that will allay any concerns about you being older and mention why you depledged, that it didn't feel like home to you and you remember how much you liked ABC before.
I wish you luck
