#!/usr/bin/perl
use warnings;
use strict;

my $test = 'test';
my %hash = ( t => \$test);        # Store the reference.

print join "\t", 'Before', ${ $hash{t} }, $test, $hash{t}, "\n";

my $change = 'changed';
${ $hash{t} } = $change;          # Change the value.

print join "\t", 'After', ${ $hash{t} }, $test, $hash{t}, "\n";

__END__
Output:
Before  test    test    SCALAR(0x600078238)
After   changed changed SCALAR(0x600078238)