ToDiracGamma67[exp] substitutes \frac{1}{2} \left(1 + \gamma^5\right) and \frac{1}{2}\left(1-\gamma^5\right) by the chirality projectors \gamma^6 and \gamma^7.
Overview, DiracSubstitute5, DiracGamma, ToDiracGamma67.
GA[\[Mu]] . (1/2 + GA[5]/2) . GA[\[Nu]]
ToDiracGamma67[%]\bar{\gamma }^{\mu }.\left(\frac{\bar{\gamma }^5}{2}+\frac{1}{2}\right).\bar{\gamma }^{\nu }
\bar{\gamma }^{\mu }.\bar{\gamma }^6.\bar{\gamma }^{\nu }
When the option All is set to True, also standalone \gamma^5 will be replaced
GA[\[Mu], 5, \[Nu]]
ToDiracGamma67[%, All -> True]\bar{\gamma }^{\mu }.\bar{\gamma }^5.\bar{\gamma }^{\nu }
\bar{\gamma }^{\mu }.\left(\bar{\gamma }^6-\bar{\gamma }^7\right).\bar{\gamma }^{\nu }