Accurate atomic data and reliable spectroscopic diagnostics for tungsten are essential for fusion research, given its role as a plasma-facing material in ITER. We present a systematic study of highly charged W31+–W39+ ions, combining large-scale atomic structure calculations with collisional–radiative modeling under fusion-relevant conditions. Excitation energies and magnetic dipole (M1) transition probabilities were calculated using the Flexible Atomic Code with extensive configuration expansions, achieving excitation energy deviations within 2% for W31+ and W35+–W39+. Larger discrepancies for W32+ and W34+ reflect both the intrinsic challenges of modeling open-4d shell correlations and uncertainties in available experimental benchmarks. The CR model, incorporating dielectronic recombination, accurately reproduces charge-state distributions at eV and cm−3 consistent with Large Helical Device observations. Synthetic spectra in the 500–900 Å vacuum ultraviolet range successfully reproduce 11 experimentally observed lines and resolve several previously ambiguous spectral assignments. Importantly, selected M1 intensity ratios exhibit strong, distinct sensitivities to electron temperature and density, establishing them as robust diagnostics for tungsten impurity monitoring. This work provides comprehensive atomic data and validated spectral interpretations that enhance tungsten modeling accuracy and support plasma diagnostics development for ITER and future fusion devices.