1) A break even rule makes no sense in my opinion. in 95% of all cases the NT manager is just doing his job that his peers have elected for him to do. Sure there is the other 5% that could be abusing their power, but I feel like the general public would abuse this right to see one of the NT manager's players much more than the NT coach.
2) With the varying strengths of all the nations in BB and once again, the use of tracking players training and skill progression, I don't believe there is a viable option to implement this to work well.
3)
One damage is still a damage - Even if one team will be exploited, it is enough for handling this.
Waiting season and an half may be OK for you, but that manager may quit.
I'm a little confused. Which manager are you talking about? The NT manager or the manager with the NT player? In both aspects, I still don't understand the issue. If they quit, they quit, but I highly doubt these actions that you are talking about become a cause for a manager to quit the game. Butterfly effect although being an interesting take on things, I also don't believe is actually an issue. Knowing the skills of one player will not likely be the reason for a win or loss.
4) Uh, what? It is the same exact situation, so I don't think you can play it off as if it is different. NT players might not be that important on that team either then.
My favorite analogy to your argument:If one person gets drunk and beats someone to death with a tuba that they found on the street for an unknown reason, You don't take away all the tubas in the world and you don't take away all the alcohol, you just punish the individual for not doing what they were suppose to. You are suggesting the opposite and saying that NT managers shouldn't be able to see players to evaluate them or have to have other rules put in place to control them, simply because one manager is abusing his power. This is much like taking tubas and alcohol away from the general public simply because one psycho was making poor decisions. If that makes sense.

Murray/Harris/MPJ/Grant/Jokic - 2020 NBA Champs