Tuning the global eigenfrequencies of bounded elastic structures typically requires modifying external geometry or bulk material properties, intrinsically coupling resonance control to the object’s size and boundary conditions. Here we demonstrate control of global flexural eigenmodes using subwavelength internal architecture in a metamaterial xylophone that operates in the long-wavelength effective-medium regime, without altering the external envelope of each unit. Periodic internal air-slot lattices are embedded beneath the vibrating plate of a finite elastic resonator and reduce its effective bending stiffness while preserving modal topology and boundary conditions. Finite-element calculations show that the fundamental flexural eigenfrequency scales predictably with architecture-controlled reductions in effective stiffness, while values of the Modal Assurance Criterion confirm invariance of the global mode shape. We construct a compact surrogate model to describe the dependence of resonance frequency on slot depth, slot-width ratio, and number of cells. Measurements on additively manufactured prototypes agree with the predicted scaling and demonstrate continuous eigenfrequency tuning over a full octave across two external sizes. These results establish architectural homogenization as a general strategy for eigenmode engineering in finite elastic bodies, decoupling resonance control from external geometry and enabling the design of space-constrained resonant structures.