Append new data to existing XML for output?

[Rich Wallace]

I'm sure there's a very weasy way to do this, I've been running hard and
fast on several things at once and just may be at the point of overthinking
this...

I receive an incoming XML document via a string feed within a web service:

<Root>
<Product>
<File>Order</File>
<Origin>OregonOffice</Origin>
<Details Name="Product" Value="Binder" />
<Details Name="Qty" Value="1" />
</Product>
</Root>

I need to modify the outgoing XML to read the status of an approval check:

<Root>
<Product>
<File>Order</File>
<Origin>OregonOffice</Origin>
<Details Name="Product" Value="Binder" />
<Details Name="Qty" Value="1" />
<Details Name="Approved" Value="False" />
</Product>
</Root>

Once I have the True or False value from a method call, how would I modify
the XML to add the new attributes?

TIA
-Rich