From: London, Surrey, United Kingdom
You'd need to edit the scenario and change the number of turns.
You can (or could) open a save game in the editor by changing the file extension. However, if you go down this route you'll need to ensure you modify all the events, reinforcement arrival times, replacements schedule and calendar, to reflect the fact that if you open the scenario again it will be turn 1 again.
Anyway, scenario duration is an important element of balance. If you lost the scenario, it's because in the designer's opinion you've either not done enough to win the campaign, or have been outperformed by your historical counterpart. As the attacker, giving yourself extra turns will lead to you "winning"- but this doesn't signify much. Of course it's possible the designer got this wrong. We are only human after all.
To take Barbarossa as an example, the scenario will not have events or units which reflect the further buildup of the Red Army after the end of the scenario. As such, the German player will have an unrealistic advantage while playing on. Further, winter won't end: there are no events for a warm front (with attendant mud) to arrive in the Spring. I wouldn't recommend extending the scenario. If you want to play the same campaign over a longer period, pick another scenario, or better yet design your own from scratch.
< Message edited by golden delicious -- 11/24/2012 1:11:00 AM >