I posted this as a side point in the WoT mod thread, but maybe someone here can answer it:

If we could change the number of turns in one year that would be awsome. For example, have four seasons to a year instead of two.

I was thinking of a possible way of doing this. I was looking around the prologue_script.txt file, and I noticed that you can enter cheats. They use the line console_command, and then enter the cheat code.

For example, they make sure you don't lose ur character by making him invulnerable:

console_command invulnerable_general "Gaius Julius"

If we could somehow make this type of script work for other campaigns, then you could write out a very long script which would do this:

Turn one: do nothing (spring)
Turn two: change the season back to summer (summer)
Turn three: change the season back to summer (autumn or fall for the americans)
Turn four: do nothing. (winter, the date would then automatically advance by one at the end of this turn)

It would do this in cycle for the whole game period, and there you go, four turns to a year.

Now I don't know if it would work, but its an idea worth looking into.