In ionic nanocrystals the cationic sublattice can be replaced with a different metal ion via a fast, simple, and reversible place exchange, allowing postsynthetic modification of the composition of the nanocrystal, while preserving its size and shape. Here, we demonstrate that, during such an exchange, the anionic framework of the crystal is preserved. When applied to nanoheterostructures, this phenomenon ensures that compositional interfaces within the heterostructure are conserved throughout the transformation. For instance, a morphology composed of a CdSe nanocrystal embedded in a CdS rod (CdSe/CdS) was exchanged to a PbSe/PbS nanorod via a Cu2Se/Cu2S structure. During every exchange cycle, the seed size and position within the nanorod were preserved, as evident by excitonic features, Z-contrast imaging, and elemental line scans. Anionic framework conservation extends the domain of cation exchange to the design of more complex and unique nanostructures.