I tried to implement my solution with tying, too. The difference to your solution is there's no need to indicate what value you want: Perl just does what you mean, as usually: 
#!/usr/bin/perl
use warnings;
use strict;

{   package MagicScalar;
    use Tie::Scalar;
    use parent qw( -norequire Tie::StdScalar );
    use overload
        nomethod => \&stringify;

    sub TIESCALAR {
        my $class = shift;
        bless [], $class
    }

    sub STORE {
        my ($self, $value) = @_;
        $self->[0] = $value;
    }

    sub FETCH {
        my $self = shift;
        return $self
    }

    sub stringify {
        my $self = shift;
        return $self->[0]
    }
}

{   package MagicHash;
    use Tie::Hash;
    use parent qw( -norequire Tie::StdHash );

    sub STORE {
        my ($self, $key, $value) = @_;
        my $previous = $self->{$key};
        if (ref $previous and $previous->isa('MagicScalar')) {
            $previous->STORE($value);
        } else {
            $self->{$key} = $value
        }
    }
}

tie my $test, 'MagicScalar';
$test = 'test';

tie my %hash, 'MagicHash';
%hash = (t => $test);

print "Before $hash{t} $test\n";

my $change = 'changed';
$hash{t} = $change;

print "After $hash{t} $test\n";

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لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

In reply to Re^3: Changing a variable which is a value of a hash by choroba
in thread Changing a variable which is a value of a hash by benedicth

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