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