SMART-Editor is a framework for constructive layout and content editing in both structured (posters, websites) and unstructured (natural image) domains. Unlike existing models that perform local editing, SMART-Editor maintains global consistency through two strategies: Reward-Refine, an inference-time reward-guided refinement method, and RewardDPO, a training-time preference optimization approach that uses reward-aligned layout pairs. To evaluate model performance, we introduce SMARTEdit-Bench, a benchmark that encompasses multi-domain, cascading editing scenarios. SMART-Editor outperforms strong baseline models such as InstructPix2Pix and HIVE, with RewardDPO achieving up to 15% performance gains in structured settings, and Reward-Refine demonstrating its advantage on natural images. Automatic and human evaluations confirm the value of reward-based schemes in generating semantically consistent and visually aligned edits.