Spinels are an important class of compounds in energy-dense multivalent batteries with potential cathode (MgMn₂O₄) and solid electrolyte (MgIn₂S₄) applications. Both MgMn₂O₄ and MgIn₂S₄ are susceptible to inversion, which is the exchange of Mg and metal (Mn/In) sites in the spinel framework. Using first-principles calculations, we evaluate the impact of spinel Inversion, which can directly lead to several distinct local cation environments, on Mg²⁺ mobility. While activation barriers for various cation decorations determine the active Mg²⁺ diffusion channels on the atomic scale, the macroscopic migration of Mg²⁺ is essential for (dis)charge of cathodes or ionic conduction in solid electrolytes. Subsequently, we perform Monte-Carlo simulations to estimate the minimum Mg concentration required to ensure Mg²⁺ percolation through the spinel structure. Finally, we analyze the influence of inversion on the electrochemical properties of the MgMn₂O₄ cathode by investigating the phase behavior, average voltages and extractable capacities at various degrees of inversion.