(This method can be used in the vanilla version)
Also I recommend you that to make a confederation you should be using the money cheat to be easier.
My tactic is that in two turns more or less I make big presents(the most expensive ones) and when this allie has reached like 120 or something like that you can start making a confederation with a big amount of money like 80000 or more.
Start putting some 0's in the end until you have high probability in that diplomacy task.
If you don't have a friend in the other side it doesn't matter the amount of money, you will have always low probability.
I don't know what really happens to you becouse those examples are very different
Mega movement case:
It is activated forever or at least until you click once more the cheat
Isn't the case that you explained and it works perfect if when you activate it that unit has some movement becouse this effect happens after the unit has been moved by replenishing it's movement capacity
One turn unit case:
The cheat is designed like that becouse thae effect can go to places that you don't want if you leave activated.
In this case this one has a auto deactivate feature that is launched 5 seconds after the activation.
Maybe you could think that is very short but I think that is more than enough
I would reccomend you to use it like this.
Imagine that you want 19 units for one lord, you can recruit the first 18 soldiers without the cheat and the last one with the cheat
The effect is applied to all of them
The same happens in the one turn building
You can have missions that require you to maintain high public order in a province. For some reason there seems to be no way to turn this mode off in a particular save once it has been activated, even after restarting the game with the trainer turned off.