Multi-layer square-planar nickelates provide a rare platform in which the nominal Ni valence, dimensionality, and layer-resolved electronic structure can be tuned within the same structural family. Recent experiments have found superconductivity in n=4--8 Rₙ₊₁NiₙO₂ₙ₊₂ compounds, with the highest T_c near n=6, whereas the more heavily hole-doped n=3 member remains nonsuperconducting. Here we propose spacer-layer Cl doping as a route to convert low-n nickelates into superconducting candidates. Compared with changing the layer number n, Cl substitution on the spacer-layer oxygen sites offers a chemically natural way to continuously tune the Ni valence while leaving the NiO₂ planes largely intact; the lower-n compounds may also be more accessible for synthesis. Using density functional theory combined with dynamical mean-field theory, we show that electron-compensated n=2 and n=3 La-based nickelates, targeted to the nominal Ni valence of superconducting n=6, develop Ni-d correlations comparable to those of superconducting higher-n compounds while preserving the characteristic low-energy Ni-d electronic structure. These results suggest spacer-layer Cl doping as a promising strategy for designing low-n square-planar nickelate superconductors.