<p>This study investigates how designation under the Globally Important Agricultural Heritage Systems (GIAHS) program, together with associated conservation measures, affected agricultural landscape restructuring and ecosystem service supply–demand relationships in the Yuanyang Hani Rice Terraces, Yunnan Province, China. Using data from 2000 to 2020, the analysis distinguishes the pre-designation period (2000–2010) from the post-designation period (2010–2020). Geo-informatic Tupu analysis and landscape indices were used to characterize cropland transitions and landscape restructuring. Meanwhile, InVEST-based ecosystem service assessment, Sen–MK trend analysis, and PSM-DID estimation were combined to identify policy-related ecological effects. The results indicate that GIAHS designation strengthened the spatial differentiation between the core and non-core conservation areas. In the core area, paddy-field decline and fragmentation were effectively moderated, and landscape continuity improved. In the non-core area, cultivated land loss and non-agricultural land conversion remained more evident. Ecosystem service supply–demand relationships also diverged after designation. By 2020, the core area showed a clear improvement in the integrated supply–demand ratio, although individual ecosystem services followed different trajectories: the water conservation supply–demand ratio declined, the soil conservation supply–demand ratio increased, and habitat quality and carbon storage remained comparatively stable. The Sen–MK and PSM-DID results further confirm that the 2010 GIAHS designation marked an important turning point in the ecological evolution of the Hani Rice Terraces. These findings indicate that heritage-site conservation reshapes agricultural land-use trajectories and ecological supply–demand conditions, providing evidence for adaptive management of terraced heritage landscapes.</p>