I decided to add the MU FARL after all, if you want to support it on your end. All you need to do is change FARL.lua:240 to:

''if loco.name == "farl" or (game.active_mods["MultipleUnitTrainControl"] and loco.name == "farl-mu") then''

Will be added in the next update (maybe tomorrow)

Your change to not kick players out when replacing locos will cause the gui to disappear if the player is in a FARL, but that is my problem. They will just have to get out and back in to fix it until i manage to do it on my side.

You must be following my source on GitHub. I was planning to release the player-reinsertion update today and was surprised you knew about it.

There's not some event I could trigger that would make it transparent to you, is there?

Okay, MU Control 0.1.7 will work with FARL as soon as you release the next update. Thanks!

I think Factorio already triggers on_driver_changed_state, it's most likely just a matter of adding a new condition to my handler for it.