use XML::LibXML qw(:all);

my $parser = XML::LibXML->new();
# this could also be parse_string
my $xmldom = eval { $parser->parse_file($file) };
if ($@) {
    # problem parsing, die $@, etc.
}

# this is the outermost element
my $doc = $xmldom->documentElement;

# the rest might be familiar if you've used
# the DOM in JavaScript

# findnodes is very useful, but hard to find
# (look in XML::LibXML::Node); this assumes there's
# XML like  <asset><story>...</story><story>...</story></asset>
my $xpath = 'asset/story';    # this can be whatever XPath
my @story_nodes = $doc->findnodes($xpath);
foreach my $story_node (@story_nodes) {
    my $id = $story_node->getAttribute('ID');

    # this is an example where DOM can be annoying
    my ($uri_node) = $story_node->getChildrenByTagName('URI');
    $uri_node->normalize();
    my $uri = $uri_node->firstChild->getData();   # should 1st check it's ::Text !
    $uri =~ s/^(http://)[^.]+(\.example\.)/$1new$2/;
    $uri_node->setData($uri;

    # ....
}

# another thing not so obvious, this is in ::Document
# there are several variations, toFH, toString, etc..
$doc->toFile($newfile);