Regulation of morphology and composition of multi-component metal chalcogenide nanocrystals inculcate distinct chemical and physical properties enabling significant advances in energy storage applications.^1,2 In multi-elemental systems, the subtle reactivity balance of multiple precursors allows metal-semiconductor heterostructure formation from pre-formed metal seeds. Also, the monophasic multicomponent metal chalcogenide nanocrystals develop dynamically from the binary metal chalcogenide seeds with the subsequent incorporation of additional metal cations from solution during the growth process.³ Therefore, regulation of the seed transformation chemistry in solution will further permit greater control of the reaction mechanism to achieve various morphologies and multinary compositions. We show that forming an intermediate lamellar Cu-thiolate complex and tuning its relative stability using alkyl phosphonic acids is crucial to enabling controlled heteronucleation to form Bi-(Cu_2-xS)_n heterostructures with a tuneable number of Cu_2-xS stems on a Bi core. The denticity of the phosphonic acid group, concentration, and chain length of alkyl phosphonic acids are critical factors determining the stability of the Cu-thiolate complex. Increasing the stability of the Cu-thiolate results in single Cu_2-xS stem formation, and decreased stability of Cu-thiolate complex increases the degree of hetero-nucleation to form multiple Cu_2-xS stems on the Bi core. We also exploit the metal seed for the first time as active alloying nuclei to form colloidal Cu-Bi-Zn-S nanorods (NRs) from Bi-seeded Cu_2–xS heterostructures. The evolution of these homogeneously alloyed NRs is driven by the dissolution of the Bi-rich seed and recrystallization of the Cu-rich stem into a transitional segment, followed by the incorporation of Zn²⁺ to form the quaternary Cu-Bi-Zn-S composition. The variation of Zn concentration in the NRs modulates the aspect ratio from ~3 to ~10. Similarly, the transformation of Bi seeds is utilized to synthesize colloidal NaBi_1-xSb_xSe_2-yS_y NCs. We show that after Se addition, ternary NaBiSe₂ NCs initiate with Bi⁰ NC formation, and the Bi NCs transform gradually into rectangular shaped S-doped NaBiSe₂ NCs. Furthermore, we extend our methods to substitute Sb in place of Bi and S in place of Se. Our findings show the rectangular morphology transforms into spherical shape upon increased Sb substitution, and the S incorporation promotes elongation along <111> direction. This study highlights the potential of metal seed transformation as a direct growth route to achieving compositions modulated multicomponent NCs that are not possible by conventional direct methods or post-synthetic transformations.