Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Operator
VP_TONEMAPPING_OPERATORParameter: Scale
VP_TONEMAPPING_SCALEParameter: Exposure
VP_TONEMAPPING_EXPOSUREParameter: ISO
VP_TONEMAPPING_SENSITIVITYParameter: F-Stop
VP_TONEMAPPING_FSTOPParameter: Gamma
VP_TONEMAPPING_GAMMAParameter: Pre-Scale
VP_TONEMAPPING_PRESCALEParameter: Post-Scale
VP_TONEMAPPING_POSTSCALEParameter: Burn
VP_TONEMAPPING_BURN