$RenameFeynCalcObjects specifies a list of replacement rules that allow to rename FeynCalc objects on the fly to avoid conflicts with other package before FeynCalc is loaded (monkey patching). The value of $RenameFeynCalcObjects must be specified before loading FeynCalc.
The following code (when executed on a fresh kernel with the last two lines uncommented) allows to load FeynCalc and Roman Lee’s LiteRed on the same kernel without shadowing
$RenameFeynCalcObjects = {"MetricTensor" -> "FCMetricTensor", "Factor1" -> "FCFactor1", "Factor2" -> "FCFactor2"};
(*
<<FeynCalc`
<<LiteRed`
*)