use strict;
use XML::Rules;

my $filter = XML::Rules->new(style => 'filter', rules => {
    ADD_USER => sub {
        my ($tag, $attrs) = @_;
        delete $attrs->{USER_NAME};
        delete $attrs->{PASSWORD};
        return $tag => $attrs;
    }
});

$filter->filter(\*DATA);

__DATA__
<RIBCL VERSION="2.1">
 <LOGIN USER_LOGIN="Administrator">
  <USER_INFO MODE="write">
  <ADD_USER USER_NAME="John Smith" USER_LOGIN="jsmith" PASSWORD="%user_password%">
  </ADD_USER>
  </USER_INFO>
 </LOGIN>
</RIBCL>