Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Shell
GENERATOR_SELECTION_POLYGON_SHELL
Parameter: Start Cap
GENERATOR_SELECTION_POLYGON_CAP_START
Parameter: End Cap
GENERATOR_SELECTION_POLYGON_CAP_END
Parameter: Start Bevel
GENERATOR_SELECTION_POLYGON_BEVEL_START
Parameter: End Bevel
GENERATOR_SELECTION_POLYGON_BEVEL_END
Parameter: Start Shell
GENERATOR_SELECTION_EDGE_SHELL_START
Parameter: End Shell
GENERATOR_SELECTION_EDGE_SHELL_END
Parameter: Start Cap
GENERATOR_SELECTION_EDGE_CAP_START
Parameter: End Cap
GENERATOR_SELECTION_EDGE_CAP_END
Parameter: Start Step
GENERATOR_SELECTION_EDGE_STEP_START
Parameter: End Step
GENERATOR_SELECTION_EDGE_STEP_END