In the last few years, the effect of strain on the optical and electronic properties of MoS2 layers has been deeply studied. Complex devices have been designed where strain is externally applied on the 2D material. However, so far, the preparation of a reversible self-strainable system based on MoS2 layers has remained elusive. In this work, spin-crossover nanoparticles are covalently grafted onto functionalized layers of semiconducting MoS2 to form a hybrid heterostructure. We use the ability of spin-crossover molecules to switch between two spin states upon the application of external stimuli to generate strain over the MoS2 layer. This spin crossover is accompanied by a volume change and induces strain and a substantial and reversible change of the electrical and optical properties of the heterostructure. This strategy opens the way towards a next generation of hybrid multifunctional materials and devices of direct application in highly topical fields like electronics, spintronics or molecular sensing.