This guide contains both information for begineers of SimAirport and advanced information for advanced PC users.

Sim Aiport offers several ways to play the game:
-Career mode: This is the hardcore mode, where you have no access to the tools that make the gameplay quicker and simpler.
-Sandbox mode: This is the softcore mode, where you have access to tools that make the gameplay quicker and simpler (ability to toggle infinite money on, ability to toggle instant build on, etc...).
-Tutorials: This are a series of tutorials that do an average job at explaining how the game works (oddly enough I recommend you start with Sandbox mode as it is, in my opinion, the easier way to understand the game, at least that is how I learned the game).
-Scenarios: Built a scenario using the tool provided by the game in the scenario editor. You can set goals to achieve as well as losing conditions.

So you accidentally chose the wrong game mode but do not want to lose your Airport you worked so hard to design?
You download a Steam Workshop Airport you liked but it is not in the game mode you want?

Do not worry as you can still recover you save game, correcting this unwanted things.
All you need is a basic text editor (Notepat or Notepad++) and editing a single line of text inside your save game .AIRPORT file which is located in the following path (by default): "your drive letter:"\Users\"your username"\AppData\LocalLow\LVGameDev LLC\SimAirport\SavesDir
Using the locate word feature (Ctrl+F) after opening the file with a text editor you locate the word "sandbox". You should find a status next to it (true or false). If its true it means the game is set in sandbox mode, while if its set to false it means the game is set to career mode. Change this line accordingly to what you want then save the file.

Editing the save file to fix the error that prevents an Airport downloaded from the Steam workshop from being re-uploaded to the Steam workshop, codenamed "Steam ownership could not be verified".

All you need is a basic text editor (Notepat or Notepad++) and editing a single line of text inside your save game .AIRPORT file which is located in the following path (by default): "your drive letter:"\Users\"your username"\AppData\LocalLow\LVGameDev LLC\SimAirport\SavesDir
Using the locate word feature (Ctrl+F) after opening the file with a text editor you locate the word "SteamPublishedFileID" or "SteamPublishedFileIDEx". You should find a status next to it (numeric value). Simply set this numeric value to 0 then save the file.

FAQ:
-Is this method safe?
Yes, your save file will still load after editing the file (however backing up your saves before doing it never hurts).

-Will this reset my progress?
No, it will not (however it is recommended to make sure you save the game you wish to edit before without any building pending orders, if you plan on changing from career mode to sandbox mode. As this may cause unforseen consequences due to the differences between both modes in regards to building, if your game has instant build already active in sandbox mode).

-Will this break my PC?
Absolutely not, you are not injecting malicious code, downloading a virus (or anything in fact). You are simply editing some text in an isolated file.

-Is this method fullproof?
I am glad to say, yes. However, be very mindful that its safer to close the game entirely and disabling the Steam cloud (if it is enable), again, to prevent some unforseen consequences.

-Will the dev team be able to recover your broken saves?
No, they may not (without a save file backup). That is why you need a save file backup before attempting the save file editing method to roll back to in case something happens. If your save file does get corrupted (because of say, a Steam issue) the devs may not be able to recover them for you as well (without a save file backup) so a save file backup is necessary to roll back to.

-Bonus: How do I get rid of the negative funds in sandbox mode?
This is most likely caused by activating infinite money on a save file that has no balance itself (which means it was always played with Infinite money right from the very start). You will need to load your save file into the ingame scenario editor and set the funds to whatever balance you wish (from 450.000 to up to 5.000.000) then save the game again. Do not change anything else other than the money, otherwise you will convert that save file into a scenario once you save it the next time.

I hope my little guide has helped you recover some playtime and enjoy the game to its fullest potential. Happy Airport building and management and thank you very much for taking the time to read my guide. I will keep updating the information if anything changes, as always, with my guides.