Addressing climate change and sustainable development remains a persistent global and national challenge. This paper responds to the need for integrated national transformation pathways, informed by a participatory co-creation process. We apply a stakeholder-guided system dynamics modelling approach using the iSD-AT model to analyse two scenarios: a baseline scenario reflecting less ambitious energy and climate policies, and the stakeholder-driven Co-SDG scenario that integrates climate change mitigation goals (SDG13) with other Sustainable Development Goals (particularly SDGs 1, 7, 8, 10 and 12). Translating co-created policy measures into quantitative modelling enabled us to explore an integrated scenario targeting multiple sustainability goals and combining a diverse set of policy measures, including policies rarely represented in quantitative modelling. At the same time, the process revealed important limitations and blind spots of quantitative models, as stakeholders emphasised institutional and governance dimensions that are only partially captured in such frameworks. The Co-SDG scenario results highlight strong interdependencies between economic and environmental dynamics, showing that stabilizing real GDP per capita improves environmental outcomes, including lower greenhouse gas emissions, underscoring the need to rethink the role of economic growth within the SDG framework. Policies primarily targeting social objectives mitigate negative effects associated with lower economic growth. Finally, the analysis highlights the importance of accounting for synergies among interacting policy measures, which evolve and intensify over time, to mitigate unintended adverse effects, particularly over the long term.