Some people said that the USCIS would ignore your reschedule request and consider that you want to "give up" your GC application. Some people said that the reschedule would take 6 months long to process. I don't know how to deal with this things.
But today I will have an Infopass and I would try to ask the IO and post the answer. (As you know, don't expcet the Infopass too much because most of the IO there know nothing)