The only solution is see is to modify the save game files, and those are encrypted and not possible to modify unless someone makes a program for it.
You should just play the missions again.
I completed the campaign twice once on regular, once on veteran when I knew the missions before the game was released. I got my copy 5 days early. I took me less than 24 hours (real time, not playtime) to complete the campaign, it's not that hard.