PauliIndexNames is an option for FCFAConvert, FCCanonicalizeDummyIndices and other functions. It renames the generic dummy Pauli indices to the indices in the supplied list.
Overview, FCFAConvert, FCCanonicalizeDummyIndices, DiracIndexNames, LorentzIndexNames.
PCHN[CSI[a], i, j] PCHN[CSI[b], j, k]
FCCanonicalizeDummyIndices[%]\left(\overline{\sigma }^a\right){}_{ij} \left(\overline{\sigma }^b\right){}_{jk}
\left(\overline{\sigma }^a\right){}_{i\text{FCGV}(\text{pi251})} \left(\overline{\sigma }^b\right){}_{\text{FCGV}(\text{pi251})k}
PCHN[CSI[a], i, j] PCHN[CSI[b], j, k]
FCCanonicalizeDummyIndices[%, PauliIndexNames -> {l}]
\left(\overline{\sigma }^a\right){}_{ij} \left(\overline{\sigma }^b\right){}_{jk}
\left(\overline{\sigma }^a\right){}_{il} \left(\overline{\sigma }^b\right){}_{lk}