David Kopel at the Volokh Conspiracy answers the questions "Is Resisting Genocide a Human Right?" in the affirmative in a recent paper.
Kopel's premise, as explained in the opening of the paper essentially runs like this: A positive rule against genocide exists in international law, this rule can't be considered an effective right (as opposed to a nominal right) without a remedy. The regular enforcement of international laws against genocide are spotty at best, as such, each individual possesses a broader right against being a victim of genocide that includes taking up arms against those intending to perpetrate genocide against your people (and presumably yourself).
Obviously this premise has considerable support in domestic legal theory. Someone being threatened with murder has a right to self-defense which acts as a defense to a charge of murder. The next natural question is how this right is extrapolated to other "rights" under international law. The domestic law extrapolation is demonstrated by a right of property owners to expel trespassers with non-lethal force. Does this extrapolation follow in international law? I don't think there is a niced canned answer to this, but I suspect that the answer would generally be that it depends on the clarity of the international rule barring certain state actions and the gravity of the actions being opposed. For example, the mere fact that the source of an international law is customary rather than treaty based would imply that the parameters of that law are more difficult to ascertain, and, as such more difficult to create a right of opposition.
Anyway, I encourage all to read Kopel, et. al.'s paper and form your own conclusions.