ORIGINAL: Lobster
If you are going to do this:
Special rules for Finland
Throughout the war Finland kept close ties to the Western Allies, and never signed a formal alliance with Germany. In the game this means that if the Russians tries to conquer Finland before turn 214 by taking a hex with a red star the USA, will reduce Lend Lease to Russian (-2 supply to Russia). In addition the German units in Norway will activate and can be sent to support Finland. These effects are cancelled if the Finns or the Germans take any hex between (268,89) and (274,101) on the Kirov rail line or on turn 214 whichever comes first.
Then you have to do it completely, not just for one side. The Finns MUST stop their offensive in first week of November along the entire front. That was part of the U.S. demands and the Finns did stop. So if you want to get historical do it for both sides, not just one.
From Wiki:
Finland maintained good relations with a number of other Western powers. Foreign volunteers from Sweden and Estonia were among the foreigners who joined Finnish ranks; Infantry Regiment 200, called soomepoisid ("Finnish boys"), mostly comprised Estonians, while the Swedes mustered the Swedish Volunteer Battalion.[110] The Finnish government stressed that Finland was fighting as a co-belligerent with Germany against the USSR only to protect itself and that it was still the same democratic country as it had been in the Winter War.[98] For example, Finland maintained diplomatic relations with the exiled Norwegian government and more than once criticised German occupation policy in Norway.[111] Relations between Finland and the United States were more complex; the US public was sympathetic to the "brave little democracy" and had anti-communist sentiments. At first, the United States sympathised with the Finnish cause, but the situation became problematic after the Finnish Army crossed the 1939 border.[112] Finnish and German troops were a threat to the Kirov Railway and the northern supply line between the Western Allies and the Soviet Union.[112] On 25 October 1941, the US demanded that Finland cease all hostilities against the USSR and withdraw behind the 1939 border. In public, President Ryti rejected the demands, but in private, he wrote to Mannerheim on 5 November asking him to halt the offensive. Mannerheim agreed and secretly instructed General Hjalmar Siilasvuo and his III Corps to end the assault on the Kirov Railway.
It is already implemented: In FITE2 the Finns have never been allowed to move beyond the Yellow Diamond marked hexes (marking their historical advance). The only exception is around Louhki (270,90), where the Finns are allowed to cut the Kirov rail line, which they did not do historically as you point out.
But with the new update, the Finns pay a price for cutting the Kirov rail line. If they do that the Russians can with no penalty attack and destroy the Finns before the summer of 43 (after the summer of 43 there are no penalty, whether the Kirov Rail line has been cut or not).
If the Finns "agree" to the US demands, and do not cut the Kirov Rail line at Louhki, the US will, in turn, look harshly on the Russians destroying the Finns before the Summer of 43: the Russians get -2 supply for the entire war (representing reduced Lend Lease). This penalty is activated if the Russians move beyond the Red Star marked hexes.
So in short: the Russians can still destroy the Finns if they want too before the summer of 43, but it will cost them -2 supply (and the Germans in Norway will active) unless the Finns have cut the Kirov rail line around Louhki.
It is a difficult political situation to simulate in TOAW, but this is our attempt.