Huge props to @WizzardMaker for putting these decrypted CSV files out there. For the files most likely to be modded, here are a few pointers/tips I learned along the way:

routen.csv: the game doesn't seem to accept more than 185 total routes (186 lines including the header). That is about 10 additional routes compared to the original game file. If anyone figures out how to overcome this, post here! However, you can modify the other routes to your liking. Just be sure to keep the spelling of each city and formatting the same, or the game won't take it. The "Ebene" value is whether the route distance is short (1) or long (2). This value determines whether the route shows up on the in-game laptop under short or long routes.

planetyp.csv: for the "verfügbar ab" (year the aircraft became available) value, avoid using years 1996 and 1997. This caused the game not to load.

Happy modding!

The link is not valid. Can you repost please.

Thanks much for sharing! My game will not run with the new .csvs files. Any thoughts?

Here is the new link https://drive.google.com/file/d/0B36DbYtnH9spY2lNdzRoV2FpNjBUMTJ2Zm9sZTNyejlNM0pF/view?usp=drivesdk&resourcekey=0-pZwFXNGuqHwXP9c3oT6-kw