"I do not know the process first hand but once you notify your employer you are retiring, process the paperwork and start collecting benefits, it doesn't seem like you could 'un-retire' and go back to the line if the age limit is increased."
I'm sure this all will depend on what the "experts" in congress pull out of their... I mean what they think is best for their constitcheents. If they say you can un-retire, then you can un-retire.