In nanoimprint lithography (NIL), the imprinting stamp's fabrication is still a significant cost factor among the consumables. Bottom‐up lithography approaches based on a phase‐separation of polymer blends can provide a cost‐effective route for fabricating these stamps. Today's polymers used to prepare phase‐separated nanostructures (PSN), however, exhibit low glass transition temperatures. As a result, the PSN are prone to in‐plane stamp distortions in the presence of high imprinting pressure and temperature, limiting their practical relevance for NIL. Here, the realization of mechanically and thermally stable PSN‐based imprinting stamps for NIL systems via a phase‐separation of a homopolymer/inorganic–organic hybrid polymer blend is reported. It is demonstrated that these imprinting stamps are easily tunable and scalable by adjusting the formulation of homopolymer/hybrid polymer mixture and deposition conditions. Feature sizes in PSN ranging from a few μm down to 100 nm are achieved through an interplay of these factors. As demonstrations of the envisioned applications, the developed imprinting stamps are integrated into a roll‐to‐roll NIL system for patterning a polystyrene thin‐film. Moreover, light management is demonstrated by nanopatterning of a perovskite semiconductor in plate‐to‐plate process. The nanopatterned perovskite film achieves an integrated absorption and a photoluminescence emission peak increase of 7%rel and 121%rel, respectively.