use strict;
my $str = '
<div class="header-info-box">
Разный контент, <span> включая теги</span>
<div>
<div> </div>
</div>
</div>
';
my $regex = qr~<div class="header-info-box">\K((?:[^<]|(?!</?div).|<div(?1)</div>)*+)~mp;
my $subst = '<div class="hello"></div>';
my $result = $str =~ s~$regex~$subst~rg;
print "The result of the substitution is' $result\n";
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html