Interactions form the basis for the experimental generation of entanglement between quantum objects. Using all-to-all interactions, numerous experiments with atomic ensembles have generated quantum states which provide a higher precision in sensing protocols compared to unentangled states. However, many envisioned applications in quantum sensing and computation require greater control over the spatial entanglement structure and, thus, the effective graph of interactions. In our experiment, we use an optical cavity together with local spin rotations to mediate programmable long-range interactions within a 1D array of atomic ensembles. Driving the cavity with light induces all-to-all interactions between the spin-1 atoms, creating atom pairs and quantum correlations within a single spatially extended mode of the collective transversal spin. In this case, we measure spin-nematic squeezing and verify the generation of entanglement between spatially separated ensembles by quantifying the correlations in two non-commuting observables. By employing local spin rotations we selectively couple different spatial modes to the cavity and thus control the structure of the generated quantum correlations. This capability allows for tailoring the entanglement structure to a specific quantum enhanced task such as distributed quantum sensing and measurement-based quantum computation.