Although numerous polyphosphido complexes have been accessed through the transition-metal-mediated activation and functionalization of white phosphorus (P₄), the selective functionalization of the resulting polyphosphorus ligands in these compounds remains underdeveloped. In this study, we explore the reactions between cyclotetraphosphido cobalt complexes and heterocumulenes, leading to functionalized P₄ ligands. Specifically, the reaction of carbon disulfide (CS₂) with [K(18c-6)][(Ar*BIAN)Co(η⁴-P₄)] ([K(18c-6)]1, 18c-6 = [18]crown-6) affords the adduct [K(18c-6)][(Ar*BIAN)Co(η³:η¹-P₄CS₂)] ([K(18c-6)]3), in which CS₂ is attached to a single phosphorus atom (Ar* = 2,6-dibenzhydryl-4-isopropylphenyl, BIAN = 1,2-bis(arylimino)acenaphthene diimine). In contrast, the insertion of bis(trimethylsilyl)sulfur diimide S(NSiMe₃)₂ into a P-P bond of [K(18c-6)]1 yields [K(18c-6)][(Ar*BIAN)Co(η³:η¹-P₄SN₂(SiMe₃)₂)] (K(18c-6)]4). This salt further reacts with Me₃SiCl to form [(Ar*BIAN)Co(η³:η¹-P₄SN₂(SiMe₃)₃] (5), featuring a rare azatetraphosphole ligand. Moreover, treatment of the previously reported complex [(Ar*BIAN)Co(η³:η¹-P₄C(O)tBu)] (2) with isothiocyanates results in P-C bond insertion, yielding [(Ar*BIAN)Co(η³:η¹-P₄C(S)N(R)C(O)tBu)] (6a,b; R = Cy, Ph).