$userref->{2}{'hash'}{'name'} = '12345';
$userref->{3}{'hash'}{'name'} = '10foo';
[download]

I am not using XMLin for anything.

Then I would ditch XMLout ASAP :) seriously

The way I use XML::Simple, is start with XML I want, then use XMLin to get data I want, then XMLout to get back xml I started with

If XMLin can't be made into data structure you want, then XMLout can't be made into xml you want

All that massaging of $userref you do is busywork :)

So with XML::Rules ( XML::Simple on steriods :) steroids) I might write

#!/usr/bin/perl --
use strict; use warnings;
use XML::Rules;
use Data::Dump qw/ dd /;

my $wanted = <<'__XML__';
<?xml version="1.0" encoding="utf-8"?>
<opt>
  <key0>
    <devices>
      <dev0>
        <param id="name">joe</param>
        <param id="type">user</param>
      </dev0>
    </devices>
  </key0>
  <key1>
    <devices>
      <dev0>
        <param id="name">mary</param>
        <param id="type">user</param>
      </dev0>
    </devices>
  </key1>
</opt>
__XML__



use XML::Rules;
my $t = XML::Rules->new(
    qw/ stripspaces 8 /,
    rules => {
      'dev0,devices,key0,key1,opt' => 'no content',
      'param' => 'as array',
    },
);

my $XmlRef  = $t->parse( $wanted );
dd $XmlRef;
print $t->toXML( opt => $XmlRef->{opt}, undef, "  ", );
__END__
{
  opt => {
           key0 => {
                     devices => {
                       dev0 => {
                         param => [
                           { _content => "joe", id => "name" },
                           { _content => "user", id => "type" },
                         ],
                       },
                     },
                   },
           key1 => {
                     devices => {
                       dev0 => {
                         param => [
                           { _content => "mary", id => "name" },
                           { _content => "user", id => "type" },
                         ],
                       },
                     },
                   },
         },
}
<opt>
  <key0>
    <devices>
      <dev0>
        <param id="name">joe</param>
        <param id="type">user</param>
      </dev0>
    </devices>
  </key0>
  <key1>
    <devices>
      <dev0>
        <param id="name">mary</param>
        <param id="type">user</param>
      </dev0>
    </devices>
  </key1>
</opt>
[download]

You still get to have a hairy hash, you still get your xml, and you don't spend days trying to make it "Simple"

Okay, that is very interesting, and it does give you more control, granted. but i want a more on-the-fly approach, which sauoq's solution grants me. i'm not saying you can't do that with XML::Rules of course (i'm sure you can), but his simple edit to my hashref manipulation was easy and ideal and I got to keep XML::Simple and its simple ways. thanks!