Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Volume Type
ID_VOLUMEBUILDER_VOLUMETYPEParameter: Voxel Size
ID_VOLUMEBUILDER_GRID_SIZEParameter: Interior Voxel Range
ID_VOLUMEBUILDER_HALF_BAND_MESH_INTERIORParameter: Exterior Voxel Range
ID_VOLUMEBUILDER_HALF_BAND_MESH_EXTERIORParameter: Spline Voxel Range
ID_VOLUMEBUILDER_HALF_BAND_SPLINEParameter: Particle Voxel Range
ID_VOLUMEBUILDER_HALF_BAND_PARTICLEParameter: Override Grid Matrix
ID_VOLUMEBUILDER_GRID_MATRIX_OVERRIDEParameter: Match Voxel Size
ID_VOLUMEBUILDER_MATCH_GRID_BUTTONParameter: Auto Update Settings
ID_VOLUMEBUILDER_AUTOUPDATEParameter: Update
ID_VOLUMEBUILDER_UPDATEBUTTON