Floating Offshore Wind Turbines (FOWTs) promise abundant wind resources in deep waters but face structural risks due to corrosion-fatigue (CF) deterioration. The present study aims at a comprehensive framework to evaluate and mitigate the CF risk, and to optimise the operational costs and power production through incorporating strategic and window-aligned the opportunistic operation and maintenance (OOM). Multi-physics modelling and reliability assessment are applied to evaluate fracture-critical ring-flange connections at component, flange, and structural levels. On this basis, failure risk is further quantified through cost losses associated with varying failure consequences. As the key factor influencing structural vibration and power production, three turbine control strategies are examined, i.e., a reference strategy and two de-rating strategies with varying operational reductions. Based on these risk-informed insights, a Genetic Algorithm (GA)-driven, co-scheduled OOM framework is proposed to optimise both turbine control strategies and maintenance actions in an integrated manner. The results highlight the critical impact of CF deterioration on the structural reliability and risk over a 25-year service life. Meanwhile, the de-rating control strategy is validated in mitigating the structural risk and extending maintenance intervals. By coupling operation strategies with maintenance actions in a risk-informed and window-aligned way, a delicate trade-off can be achieved to optimise the structural risk, maintenance cost, and power production in a life-cycle context. This study provides practical insights for industry, demonstrating risk-informed OOM strategies can enhance FOWT performance and cost-effectiveness under similar design and environmental conditions. The proposed framework also sets the stage for future research on dynamic maintenance strategies in FOWT risk and reliability management.