rob, who are you kidding? We both know al pi halacha a ger must accept each and every taryag mitzvos before he can become a ger. He may not know the details of each mitzvah, but he knows he must fully accept all 613.
Secondly we both know that most of these zionist so-called converts do not accept all 613. They know that beforehand, and are kidding no one. Shabbos itself is not maintained, or intended to be maintained, by so many of them.
So as a matter of fact they never were geirim, so nothing is being retroactively annulled, but rather we are just recognizing the facts.