For anyone looking for the csv files:
Here they are!
The game will read the decrypted files just fine
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.