XML::Simple is a great tool for

• reading XML into a perl data structure
• writing a perl data structure out to XML where the actual layout doesnt matter, only the well-formedness

By that second point I mean, you aren't contrained by someone elses DTD or XSD - there layout is important e.g. the <name> element must come before the <address> element if the XSD says so, but because XML::Simple is outputting a hash with 'name' and 'address' keys, you cant control that (well, you can, but you have to tie the hash to a package that will sort the keys for you)

In my opinion, if your going to be writing elements/nodes to an XML document, and you dont want to perturb any other parts of the document, your better off using an XML module that supports XPath navigation to locate your insert point, and using its API to insert the required nodes.

This is more robust than tweaking XML::Simple's many options to keep the source and result documents the same.

Another option is XSLT, but that's a whole other technology to master...