Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Source
MDATA_REPROJECT_SOURCELISTParameter: Dest
MDATA_REPROJECT_DESTParameter: Create Copy
MDATA_REPROJECT_CREATECOPYParameter: Hide When Finished
MDATA_REPROJECT_HIDEParameter: Subdivision Level
MDATA_REPROJECT_SUBDIVISION_LEVELParameter: Project
MDATA_REPROJECT_PROJECT