Single-chain magnets (SCMs) that exhibit slow relaxation of their magnetization are attracting considerable attention. To tune the properties of such materials with external stimuli such as light, heat, and pressure is a challenge. Through the exploitation of light and heat induced transformation between diamagnetic Fe-Ls(parallel to)(mu-CN)Co-Ls(vertical bar vertical bar vertical bar) (LS = low spin) units and paramagnetic Fe-Ls(vertical bar vertical bar vertical bar)(mu-CN)Co-Hs(parallel to) (HS = high spin) units, we show the photoswitched transformation from a paramagnetic state to an antiferromagnetic ordered SCM state and the thermally induced reverse transformation, thus providing an effective way to control the spin topology of the SCM via light or a thermally induced metal-to-metal charge transfer.