Recent developments in global politics and international relations theory have raised questions about the strength of international norms. Critical constructivists identify instances of norm change, contestation, and even regress, arguing that norms may be less deeply internalized and more fragile than often assumed. This study builds on contemporary constructivist scholarship to advance a model of elite-driven norm change with stages of redefinition and substitution through contestation. It conducts a plausibility probe of the model by analyzing the development of the Proliferation Security Initiative, the US-led program that appeared designed to change normative principles from non-proliferation to counter-proliferation and from freedom of navigation on the high seas to maritime interdiction of suspect weapons and technology shipments. The model lends valuable insights on the evolution of norms to accommodate new realities over the last decade, and it suggests the need for more contingent and multi-linear theories of international cooperation.