use XML::Rules;

my $updater = XML::Rules->new(
  style => 'filter',
  rules => {
    'particular_tagname' => sub {
      my ($tag, $attr, $context) = @_;
      if (@$context == $that_depth_level
        and $attr->{this_atribute} eq 'some value'
      ) {
         do_stuff_to($attr);
      }
      return $tag => $attr;
    },
  }
);

$updater->filterfile( $infile, $outfile);