Hello Jim,
T'is not that easy in this case, at least from what I have read during Google searches so far. AFAIU there is one lone bit that gets flipped for each email. That turns one value from 2001 to 2009 (or the other way around). Doing a blanket change for all those instances is most likely guaranteed to currupt the whole big file in many places. Definitely all the ones written in 2001 :-)
According to the Mozilla site there is no parser routine for doing this and they recommend doing it by hand. That would be like knitting a
12"*12" area rug. By hand...