We presented PoreMatMod.jl as a free, open source, user-friendly, tested, and documented Julia package for modifying crystal structures. PoreMatMod.jl functions as a find-and-replace algorithm on crystal structures: given a parent crystal structure, PoreMatMod.jl ( , via Ulmann's subgraph isomorphism algorithm) searches for subgraphs of the parent that match the graph of a query fragment then ( , via orthogonal Procrustes) aligns and installs replacement fragments in place of the substructures of the parent matching the query fragment, giving a child crystal structure.