Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Enable
MDATA_SOFT_ENABLE
Parameter: Surface
MDATA_SOFT_SURFACE
Parameter: Rubber
MDATA_SOFT_RUBBER
Parameter: Restrict
MDATA_SOFT_RESTRICT
Parameter: Preview
MDATA_SOFT_PREVIEW
Parameter: Falloff
MDATA_SOFT_FALLOFF
Parameter: Mode
MDATA_SOFT_MODE
Parameter: Radius
MDATA_SOFT_RADIUS
Parameter: Strength
MDATA_SOFT_STRENGTH
Parameter: Width
MDATA_SOFT_WIDTH
Parameter: Spline
MDATA_SOFT_SPLINE