Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Text Spline
PRIM_TEXT_TEXT
Parameter: Font
PRIM_TEXT_FONT
Parameter: Align
PRIM_TEXT_ALIGN
Parameter: Height
PRIM_TEXT_HEIGHT
Parameter: Horizontal Spacing
PRIM_TEXT_HSPACING
Parameter: Vertical Spacing
PRIM_TEXT_VSPACING
Parameter: Separate Letters
PRIM_TEXT_SEPARATE
Parameter: Kerning
PRIM_TEXT_KERNING