swapping powershell xml contexts between nodes

Books.xml

<?xml version="1.0" encoding="UTF-8"?>
<bookstore>
  <book category="cooking">
    <title lang="en">Everyday Italian</title>
    <author>Giada De Laurentiis</author>
    <year>2005</year>
    <price>30.00</price>
  </book>
  <book category="children">
    <title lang="en">Harry Potter</title>
    <author>J K. Rowling</author>
    <year>2005</year>
    <price>29.99</price>
  </book>
  <book category="web">
    <title lang="en">Learning XML</title>
    <author>Erik T. Ray</author>
    <year>2003</year>
    <price>39.95</price>
  </book>
</bookstore> 

BooksPartial.xml

<?xml version="1.0" encoding="UTF-8"?>
<bookstore>
  <book category="cooking">
    <title lang="en">Everyday Italian</title>
    <author>Giada De Laurentiis</author>
    <year>2005</year>
    <price>30.00</price>
  </book>
</bookstore> 

test.ps1

#put whatever here
[xml]$good_xml = Get-Content E:\downloads\Books.xml
[xml]$part_xml = Get-Content E:\downloads\BooksPartial.xml

$book = $good_xml.bookstore.book[1]
#swap contexts
#Create a new xmlobj under the context of the other object
$new_book = $part_xml.ImportNode($book,$true)
#verify new object is indeed under the right object
$new_book.OwnerDocument -eq $part_xml
#append 
$part_xml.bookstore.AppendChild($new_book) | Out-Null
$part_xml.bookstore.book[1]
$part_xml.Save("E:\downloads\BooksPartial.xml")

#delete old book
$good_xml.bookstore.RemoveChild($book)
$good_xml.Save("E:\downloads\Books.xml")