The Chern-Simons-type term in the photon sector of the Lorentz- and CPT-breaking minimal Standard-Model Extension (mSME) is considered. It is argued that under certain circumstances this term can be removed from the mSME. In particular, it is demonstrated that for lightlike Lorentz violation a field redefinition exists that maps the on-shell free Chern-Simons model to conventional on-shell free electrodynamics. A compact explicit expression for an operator implementing such a mapping is constructed. This expression establishes that the field redefinition is non-local.
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