REACTER is a heuristic protocol that allows complex, predefined reactions to be modeled in atomistic, fixed-valence molecular dynamics (MD) simulations. The method is applicable to a broad range of chemical reactions and permits much larger and longer reactive simulations than existing approaches. One or more competing multistep reactions or series of reactions can be invoked simultaneously. Special treatment can be applied to neighboring atoms to relax high-energy configurations while the simulation progresses. The original implementation of REACTER, which was included in the open-source LAMMPS simulation package as fix bond/react, was only available for serial simulations. This work describes the expansion of the REACTER protocol for use in parallel simulations, as well as the addition of various new options, including deletion of reaction byproducts, reversible reactions, and custom reaction constraints. The capability of the parallel implementation is demonstrated through large-scale simulations (200000+ atoms) of the polymerization of polystyrene and nylon-6,6. The morphologies of both polymers are analyzed after reaching >99% extent of polymerization. Finally, the newly added reversible reactions feature is demonstrated by rupturing these highly entangled systems under uniaxial strain by defining a chain scission reaction.