##</code><code>##

_END__
Output:
Before  test    test ...
After   test changed ...

##</code><code>##


##</code><code>##

#!/usr/bin/env perl 
package MagicHash;
require Tie::Hash;
our @ISA = qw(Tie::Hash);

sub TIEHASH { bless {}, shift }
sub STORE {
    my ($self, $key, $newval) = @_;
    $self->{$key} = {key=>$key, value=>[$newval,$$newval]};
}
sub FIRSTKEY {
    my ($self) = @_;
    keys %{$self};
    my $first_key = each %{$self};
    return undef unless defined $first_key;
    return $self->{$first_key}->{key};
}
sub FETCH {
    my ($self, $key) = @_;
    my ($is_ref) = $key =~ s/^\\//;
    return $is_ref
        ? $self->{$key}->{value}->[0]
        : $self->{$key}->{value}->[1]
    ;
}
sub NEXTKEY {
    my ($self, $nextkey) = @_;
    my $next_key = each %{$self};
    return undef unless defined $next_key;
    return $self->{$next_key}->{key};
}

package main;
use strict;
use warnings;
use Data::Dumper;
{
    my $test    = 'test';
    my $changed = 'changed';
    my %hash = ( t => \$test );
    print "Before: \$test = $test\n", Dumper \%hash;
    ${ $hash{t} } = 'changed';
    print " After: \$test = $test\n", Dumper \%hash;
}
{
    my $test    = 'test';
    my $changed = 'changed';
    tie my %hash, 'MagicHash';
    %hash = ( t => \$test );
    print "Tied Before: \$test = $test\n", Dumper \%hash;
    ${ $hash{'\t'} } = 'changed';
    print "Tied After1: \$test = $test\n", Dumper \%hash;
    ${ $hash{'\t'} } = 'again';
    print "Tied After2: \$test = $test\n", Dumper \%hash;
    $hash{'t'} = \'one more';
    print "Tied After3: \$test = $test\n", Dumper \%hash;
}