I think you generally have to win to be able to decide what is just, so, I dunno, if you manage to overthrow whatever construct you are opposed to? Trying to rationlise the right to not be beholden to the laws of any given land just sounds a bit sovereign citizen to me, which I think we generally deride in most contexts.

Also, from a semantic point of view, which is what the devil's advocate question was about, I don't think individuals or even non-state actors can actually declare war on something in the international law sense of that term.