FCEnableTraditionalFormOutput[] sets the output format of the current FrontEnd to TraditionalForm. The setting is not persistent, such that it does not influence any subsequent Mathematica FrontEnd sessions.
Overview, $FCTraditionalFormOutput, FCDisableTraditionalFormOutput.
FCDisableTraditionalFormOutput[]
FV[p, \[Mu]]\overline{p}^{\mu }
FCEnableTraditionalFormOutput[]
FV[p, \[Mu]]\overline{p}^{\mu }