Which raises a question: if I download a new mod version, will it apply to an old saved game?
Nope. Only the version of the mod which is active when the game is started.
There is a cheat called "resources" that removes ALL resource costs. Will that also apply to the AI if I use it for myself?
No idea. On the other hand, I'm gonna upload 0.6 after this soak finishes, so you'll need a new game anyway.
Which means that the OTHER level 5's are underpowered (the ones that give +50% morale and +25% production).
The +25% influence one is now level 3 (the instant-flip of everything in your culture has been swapped with it, because that's by far and away the most powerful thing in the whole line). 50% morale is more useful. with the new population scaling, but might be buffed at some point.