Mid-Game Turn Adjustment?

[Cross]

During setup we can obviously go into the map screen and change the number of turns to whatever we like.

But the problem I run into quite often is say when a game set to 25 turns is still to be decided and could benefit from an extra 10 turns, or - as happened recently - a game set to 30 turns but the battle was over at turn 10, the game still had to be played for the remaining 20 turns.

I recall the surrender button didn't work out for some reason, but what about the possibility of being able to change the number of turns mid-game? A PBEM game would require a verbal agreement to change the turns, so I don't see how it could be used as a cheat.

A seperate but related question I have: Is there some file I can edit to change the initial random number of turns assigned to a game. Or is it more complex than that, with the number of turns related to force or map size or something?

Cheers,
Cross