While regime complexes, sets of overlapping institutions governing a common issue area, are frequently characterised by stable interinstitutional divisions of labour and incremental change, actor-centred approaches emphasise potentially disruptive cross-institutional strategies. I propose a conceptual framework highlighting the constraints under which states operate within regime complexes, focusing on the role of critical actors that cannot effectively be excluded from cooperation because of their contributions to international public goods and/or negative externalities that their non-participation would generate for cooperating states. Where such actors pursue conservative policy objectives, reformist actors have limited scope for employing cross-institutional strategies and cooperating through alternative club settings. This leads to incremental institutional change as those latter actors attempt to elaborate and develop pre-existing rules instead of creating new ones. I demonstrate the explanatory power of this approach for the formation of three Access and Benefit-sharing regimes within the Genetic Resources regime complex.