Localize core function. Is this good?

localize-core-function.pl

#!/usr/bin/env perl

use strict;
use warnings;

BEGIN {
    *CORE::GLOBAL::ref = sub { return "HELLO"; };
}

my $hash = {
    aaa => 1,
    bbb => 2,
};

print "hash is " . (ref $hash) . "\n";

*CORE::GLOBAL::ref = *CORE::ref;

print "hash is " . (ref $hash) . "\n";

__END__
output:
hash is HELLO
hash is HASH