Without having written any code to verify this, this seems like a most excellent use of Hash::Merge and XML::Simple.

In theory, it should be something as easy as this:

use XML::Simple;
use Hash::Merge;

my %config1 = %{XMLin ('file1')};
my %config2 = %{XMLin ('file2')};
my %newhash;
Hash::Merge::set_behavior ('RIGHT_PRECEDENT');
*newhash = merge (\%config1, \%config2);
XMLout (\%newhash, outputfile => "newfile", xmldecl => 1, rootname => 
+'config');
[download]

While this code is theoretical, I use a variant of it for a similiar purpose, and it works flawlessly. I don't know if what you want to do can be done reliably, without using some XML module or another.

--Chris