Coupling effects among mechanical, electrical and magnetic parameters in thin film structures including ferroic thin films provide exciting opportunity for creating device functionalities. For thin films deposited on a substrate, their mechanical stress and microstructure are usually determined by the composition and processing of the films and the lattice and thermal mismatch with the substrate. Here it is found that the stress and structure of an antiferroelectric (Pb0.97,La0.02)(Zr0.90,Sn0.05,Ti0.05)O3 (PLZST) thin film are changed completely by a ferroelastic strain in a magnetic shape memory (MSM) alloy Ni-Mn-Ga (NMG) thin film on the top of the PLZST, despite the existence of the substrate constraint. The ferroelastic strain in the NMG film results in antiferroelectric (AFE) to ferroelectric (FE) phase transformation in the PLZST layer underneath. This finding indicates a different strategy to modulate the structure and function for multilayer thin films and to create unprecedented devices with ferroic thin films.