Background: Engineering hydrogel scaffolds for tissue engineering requires simultaneous control of mechanical stability and microstructural permissiveness. However, in conventional bulk hydrogels, these properties are strongly coupled because the network architecture is largely defined during gelation. Here, we report a diffusion-mediated strategy that temporally separates covalent network formation from subsequent microstructural evolution in photocrosslinked gelatin methacryloyl (GelMA) hydrogels using physically incorporated Poloxamer 407 (Pluronic F127, PF127) as a transient additive. Methods: GelMA hydrogels containing physically incorporated PF127 were photocrosslinked to establish covalent networks, followed by aqueous equilibration to promote PF127 diffusion and post-gelation microstructural evolution. Structural changes were characterized using scanning electron microscopy (SEM), hydrated-state brightfield microscopy, Fourier-transform infrared spectroscopy (FTIR), and dry mass loss analysis. Oscillatory rheology evaluated viscoelastic behavior, while encapsulated C2C12 myoblast viability, proliferation, and cytoskeletal organization were assessed to determine cytocompatibility and cellular permissiveness. Results: Semi-quantitative FTIR analysis, supported by dry mass loss measurements, demonstrated substantial PF127 depletion after 24 h equilibration in 5% GelMA formulations, while preserving GelMA amide bands. SEM revealed increased apparent porosity following equilibration, whereas rheology confirmed retention of elastic-dominant viscoelastic behavior across all formulations. Remodeling was attenuated in 10% GelMA formulations, reflecting diffusion constraints imposed by higher network density. Encapsulated C2C12 myoblasts maintained high viability and exhibited increased metabolic activity over time, with G5P5 showing the greatest filamentous actin-positive cytoskeletal coverage, indicating enhanced cellular permissiveness. Conclusions: These findings establish diffusion-mediated post-gelation microstructural tuning as a compositionally adjustable strategy for enhancing hydrogel scaffold permissiveness while preserving bulk mechanical integrity, highlighting its potential for tissue engineering applications.