$s = '
<p>something something</p>
<h2>blah blah blah</h2>
<p>something something</p>
';

$before = '<h2>([^<]+)</h2>';
$after = '"<h1>$1</h1>"';

$s =~ s/$before/$after/ee;

print $s;

##</code><code>##

<p>something something</p>
<h1>blah blah blah</h1>
<p>something something</p>

Tool completed successfully