Effective synthesis of meta-stable materials challenging the thermodynamic limits will play a significant role in broadening the horizon in material designs and further explorations of their functionalities. Although d-band correlated rare-earth nickelate perovskites (ReNiO₃) have achieved promising applications, e.g., metal-to-insulator transition, artificial intelligence, and memory/logical devices, the thermodynamic instability and high vacuum-dependence in material synthesis have largely caused bottlenecks in these applications. Herein we demonstrate a vacuum-free and low cost chemical route to effectively synthesize single-crystalline ReNiO₃ thin films that further promote their device applications. It achieves high flexibility and convenience by adjusting the A-site compositions within the perovskites via single (i.e. Nd, Sm, Eu, and Gd), binary (i.e., Sm_1−xNd_x and Sm_1−xEu_x) and triple (i.e. Sm_1−x−yNd_xEu_y and Sm_1−x−yNd_xGd_y) rare-earth elements. The respective regulations in electronic structures, as probed via near edge X-ray absorption fine structure analysis, result in sharper metal-to-insulator transitions within a broad temperature range of 400 K, compared with their reported performances. Furthermore, we discover an overlooked thermistor transport behavior of ReNiO₃ within the binary A-site elements, which exhibits large temperature coefficients of resistance (>2%) across a broad range of temperatures (5–470 K). By overcoming the bottlenecks in material synthesis of ReNiO₃, the present work profoundly paves the way for device fabrication.