No it is not possible.
I'm unaware of any instances where people have stopped donating and the rank was removed. Either it takes a long time or it stays once you have donated. It might be possible to request it be removed, not really sure how it works though. (If it's automatic it's probably not easily possible)inb4 people stop donating just to have a cool forum rank : )
Check your paypal statements.On a semi-related note, how would I go about finding out how much I have donated? Just for kicks.