Although the developer might have stopped working on that mod.

Yes, or it will be eventually.

OK, good luck.
Let me tell you something I found and seems non-solvable.
There is only one rcon port. I asked the staff member, but they didn't receive my suggestion. It means, mods, and the scenario script, all the added parts have to share only one rcon port.
This limitation doesn't affect when you call game.write_to_file( or it spells something else), but it limits when you put script back into game.

Hmm, I was planning on using rcon as a "file has been saved" notification, so I'd be using rcon either way. I did notice I couldn't use async when calling from the c# side, though I thought that was just the rcon library I was using - as rcon is supposed to reply with a message ID.

I'll look into other ways of doing it, but maybe I just have the limit of "this mod must be the only rcon mod installed".

It's not a big deal. Clusterio seems stopped. I commented in their github, but 2-ish weeks have past, no reply. That mod is the only one in my knowledge which uses the rcon port.
Btw, one more small info. I just tried both 2 scenarios made by me on a server. One desyncs, the other crashes for no reason. For the desyncing one, it needs the staff member to do something in their cpp code, but they never received any suggestion from me. So, good luck. I'm not gonna spend any more time in this game.