Supermagnetic states are typically set during synthesis. Changing and retaining these states requires sustained external stimulus. Without resynthesis or continued stimulus, we show, for the first time, a reversible magneto-ionic switching between superferromagnetic (SFM) and superspin-glass (SSG) states using room-temperature Li-ion transport. We utilize the incomplete lithiation of NiO into nanoscale Ni and Li2O to switch between the states. Lithiation generates a fragmented nano-Ni network that strengthens dipolar interactions and promotes SFM order with stronger memory and higher room-temperature moments. Delithiation partially regenerates NiO and drives the system into an SSG state with higher low-temperature coercivity and sharper temperature-selective memory. The interconversion between SFM and SSG persists at all measured subsequent lithiation-delithiation cycles, creating a general framework for supermagnetic switching.