Having the Me-262 in 1942 would have caused major problems, but it wouldn't have been. Asking it without faulty engines, and enough fuel is asking a lot.
Being ready in 1944 I don't believe it could have done. It wouldn't have stopped D-Day (As the Germans didn't even know it was happening in Normandy) and the only real threat it would have caused would have been at the Bulge. Even then P-51s were still able to effectively dogfight with these things.