Node =>Type

Change the node bezier curvature type,
newNodeType is an enum, options available are smooth, free, broken

public static void Node_Type(SPData sPData, Node node, NodeType newNodeType)

Example:

// Get the first node of the branch with key 0
var node = SPData.BranchesDict[0].Nodes[0];
//Change node type to Smooth
SplinePlusAPI.Node_Type(SPData, node, NodeType.Smooth);