How to Replace one Xml Node with another in C#

You can use LINQ to Xml XElement.ReplaceWith method

// select node from one doc
XDocument xdoc1 = XDocument.Load(path_to_doc1);    
XElement one = xdoc1.Descendants("One").First(); 

// select node from another doc
XDocument xdoc2 = XDocument.Load(path_to_doc2);
XElement another = xdoc2.Descendants("Another").First(); 

// replace one xml node with another
one.ReplaceWith(another);
xdoc1.Save(path_to_doc1);