<p>How heritage cities can sustain everyday living support while preserving historical value is a central question in sustainable urban governance. Existing studies have focused mainly on heritage identification, conservation performance, or tourism development but have paid less attention to how relatively fixed heritage endowments are converted into contemporary living support. This study examines 143 national historical and cultural cities in China. It develops a fixed heritage endowment index (fixed HEI) and comparable living support indices (comparable LSI) for 2012 and 2022. Within a dual-scale framework of 5&#xa0;km grids and city/county units, Markov transition matrices, transition type profiling, and XGBoost-SHAP are combined to identify living support conversion in high-heritage resource units and its associated conditions. The share of nonzero LSI grids increased from 45.58% in 2012 to 61.27% in 2022, indicating an expansion of observable living support intensity under a harmonized POI framework rather than a precise increase in the absolute stock of facilities. In the high-resource sample, 70.22% of the HL grids remained HL, 29.78% shifted to HH, and 98.97% of the HH grids remained stable. The main model-based association structure focused on road network density, the impervious surface area ratio, and population density, and spatial lag robustness checks further revealed that neighborhood road network density provided additional explanatory information. These results show that high heritage endowments do not automatically translate into high levels of living support. This study moves research on historic cities from static resource evaluation to resource conversion diagnosis and suggests that heritage city governance should shift from resource identification to the governance of resource conversion capacity.</p>