Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Size
MDATA_BRUSH_FALLOFF_RADIUS
Parameter: Strength
MDATA_BRUSH_FALLOFF_STRENGTH
Parameter: Mode
MDATA_BRUSH_MODE
Parameter: Update Normals
MDATA_BRUSH_UPDATENORMALS
Parameter: Visible Only
MDATA_BRUSH_VISIBLEONLY
Parameter: Surface
MDATA_BRUSH_CONNECTED
Parameter: Preview
MDATA_BRUSH_PREVIEW
Parameter: Space
MDATA_BRUSH_RESTRICTION_SPACE
Parameter: X
MDATA_BRUSH_RESTRICTION_X
Parameter: Y
MDATA_BRUSH_RESTRICTION_Y
Parameter: Z
MDATA_BRUSH_RESTRICTION_Z
Parameter: Falloff
MDATA_BRUSH_FALLOFF_MODE
Parameter: Width
MDATA_BRUSH_FALLOFF_WIDTH
Parameter: Spline
MDATA_BRUSH_FALLOFF