Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Source
MDATA_REPROJECT_SOURCELIST
Parameter: Dest
MDATA_REPROJECT_DEST
Parameter: Create Copy
MDATA_REPROJECT_CREATECOPY
Parameter: Hide When Finished
MDATA_REPROJECT_HIDE
Parameter: Subdivision Level
MDATA_REPROJECT_SUBDIVISION_LEVEL
Parameter: Project
MDATA_REPROJECT_PROJECT