To date, superconductivity in fullerides has been almost exclusively tuned by (chemical or physical) pressure control of the conduction bandwidth, W at half filling. This contrasts sharply with the extensive control of the superconducting transition temperature, [Formula: see text] in atom-based superconductors such as the cuprates and iron pnictides and chalcogenides via changes in valence (bandfilling). Here, we investigate the effect of doping away from the exactly half-filled [Formula: see text] level in quaternary face-centered-cubic (fcc) — structured fulleride solids with nominal composition ([Formula: see text]Cs_x)[Formula: see text][Formula: see text] ([Formula: see text]), in which divalent [Formula: see text] ions partially replace monovalent alkali [Formula: see text]/[Formula: see text] ions. The resulting charged-modified fullerides in which the [Formula: see text] bandwidth is also varied with changing x show a dome-shaped dependence of [Formula: see text] on interfullerene separation in analogy with their half-filled antecedents. However, following electron injection beyond half-filling, the superconductivity dome is found to shift towards shorter interfullerene separations, i.e. towards increased conduction bandwidths.