It is possible. I don't recall the exact trick -it's something in your alphax.ini or another text rules file- but Petek will be along soon enough with the exact thing.
If you can't wait, try opening the .ini (Pretty sure it's not that one, though) and all the .txt files in your AC folder and searching for "500", possibly mentioning "Mission Year" or "MY". Changing it to a higher number is all it takes, once you've found it. Saving with Notepad will not harm anything as long as you make sure to back up any files you alter, just to be safe.