Solid-solid transitions are ubiquitous in nature and are important for technology. Understanding and exploiting transitions are complicated by the fact that multiple transition pathways can exist between small unit cell structures such as face-centered cubic (FCC) and body-centered cubic (BCC). By symmetry, FCC ↔ BCC transitions can occur via a pair of continuous transitions or via a discontinuous, first-order transition. However, how to, or whether it is possible to, select between pathways is unclear. Here, we use particle shape change to induce FCC ↔ BCC transitions in systems where particle valence is malleable. Though some particle shapes can eliminate metastable HCP stacking faults, we find that for both convex and concave particles, transitions are first-order.