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, T c 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 C 6 0 3 − level in quaternary face-centered-cubic (fcc) — structured fulleride solids with nominal composition ( Rb 2. 5 − x Csx) Ba 0. 5 C 6 0 (0 ≤ x ≤ 2. 5), in which divalent Ba 2 + ions partially replace monovalent alkali Rb + / Cs + ions. The resulting charged-modified fullerides in which the t 1 u bandwidth is also varied with changing x show a dome-shaped dependence of T c 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. [ABSTRACT FROM AUTHOR]