Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: PREF_THEME_TYPE
PREF_THEME_TYPEParameter: PREF_THEME_BMP
PREF_THEME_BMPParameter: PREF_THEME_BMPPIC
PREF_THEME_BMPPICParameter: Live Refresh
PREF_THEME_LIVEParameter: Reset...
PREF_THEME_RESET