If you change the start date in the startpos files from 1087, 1205 and 1321 to 087, 205 and 321, the events of the standard campaign will disappear. You also have to add the end date (see the Viking startpos), otherwise the end date will be 1453 and the events will be appearing at the same time (even the events of the Viking campaign), and the campaign will be very long!
// And the games End date..
SetGameEndDate:: 453

But if you want that the game panel shows the years 1... you have to open the Changes file in the Loc folder and change

["AD"]
{"AD %d"}

to

["AD"]
{"AD 1%d"}

The GH, Swiss and Burgundians don't appear, but I think the Papacy still work.