It should be by date as you can start the game
in three different periods.
If you don't want them to take effect remove
Compass and gunpowder from the build_prod13.txt.


With regard to the swiss if you have in the game it will
work, as for isolating them I'm not sure what you mean.
Do you have everyone ignore them or vica versa or both?
Do you want them just to behave as a minor faction?
(that's easy as it's what they do anyway)

One way or the other you have to have them.

Give them another name and hope for the best

LK