Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Auto Add Post Effect
HAIR_PREFS_SETUP_AUTOVP
Parameter: Auto Link Object
HAIR_PREFS_SETUP_AUTO_LINK
Parameter: Auto Add Material
HAIR_PREFS_SETUP_AUTO_MATERIAL
Parameter: Hair as Child
HAIR_PREFS_SETUP_TOCHILD
Parameter: Highlighting
HAIR_PREFS_HIGHLIGHTING
Parameter: Show Unrooted
HAIR_PREFS_UNROOTED
Parameter: Cursor
HAIR_PREFS_SHOW_CURSOR
Parameter: Object Modify Undo
HAIR_PREFS_OBJECT_UNDO
Parameter: Dynamics Undo
HAIR_PREFS_DYNAMICS_UNDO
Parameter: Default Preview
HAIR_PREFS_PREVIEW
Parameter: Custom
HAIR_PREFS_CUSTOMPREVIEW