use HTML::Parser;
use strict;

my $str = '<p>something something</p>
<h2>blah <<< blah blah</h2>
<p>something something</p>';

my $parser = HTML::Parser->new(default_h=> [\&handler, "tagname, text"]);
$parser->parse($str);

sub handler {
    my ($tag, $text) = @_;
	if ($tag) {
		if ($tag eq "h2") {
		     print "<h1>";
		} else {
             print "<$tag>";
        }
	} else {
		print $text;
	}
}