Natural musculoskeletal systems combine soft tissues and rigid structures to achieve diverse mechanical behaviors that are both adaptive and precise. Inspired by these systems, we propose a programming method for designing bioinspired soft-rigid robotic structures using lattice geometries made from a single material. By introducing previously unknown approaches to the geometric design of unit cells within lattice structures-based on continuous blending and superposition of existing lattice geometries-we can precisely tune stiffness and anisotropy. These designs enable the creation of three-dimensional structures with spatially varying mechanical properties, ranging from tissue-like compliance to rigid, bone-like load-bearing capabilities. Using these methods, we fabricated a musculoskeletal-inspired tendon-driven robotic elephant that integrates joints with programmable bending profiles, achieving a continuously soft trunk. Our lattice geometry generation techniques allow for over 1 million discrete configurations and infinite geometric variations, offering a scalable solution for designing lightweight, adaptable robots.