The structural phase transitions in hybrid perovskites are critical to their performance and stability, but controlling them remains a significant challenge. Here, we demonstrate that the dynamics of the low-temperature tetragonal-to-orthorhombic phase transition in laser-printed MAPbI₃ films can be controlled by tailoring additive chemistry. We show that the choice of charge control agent (CCA) directly impacts the intrinsic defect and strain landscape of the resulting film: an ionic CCA promotes a low-strain lattice that facilitates the phase transition. In contrast, a molecular CCA induces a high-strain, defect-rich lattice, which creates a high kinetic barrier that suppresses the transition and effectively “pins” the tetragonal phase. This work establishes a strategy to engineer strain and manage phase behavior in perovskite films, demonstrating that the ability to “lock” or “enable” a specific crystal phase by selecting additives provides a pathway to mitigate degradation and engineer stable, high-performance perovskite devices.