Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Sea Level
EARTHSHADER_SEAParameter: Land Level
EARTHSHADER_LANDParameter: Mountain Level
EARTHSHADER_MOUNTAINParameter: Frequency
EARTHSHADER_FREQUENCYParameter: Level
EARTHSHADER_LEVEL