If you'd have read all my answer to Alonso and not only what you want, just to say me again that I'm ignorant, you would have noticed and understood that my "abominable" suggestion was simply to leave the manager the choice to make a player open to NT or not. If he accept what i called "the risk" to say yes, than he takes all the risks, so, to answer to your dumb question: no, it would have been not possible to prevent serbian coach to call him since you said yes the first time he was called in NT. If you sell the player and the new owner check "no" to the call in NT, than he will not be available for Serbia and Serbian coach has to study new solutions.
That's all. It's not complicated.
My suggestion is to leave the choice to club managers to leave their players open to NT teams or not. If they say yes, then they accept everything from NT, until they sell the player. If they say no, as I would like to be able to do, then NT coaches can go f-something themselves and look elsewhere. As simple as that.