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

my %fnr = (
    COMPANY_CODE => 'AB',
    COMPANY_NAME => 'ABC, Inc.',
);
my %fnr_loop = (
    COMPANY_CODE => 'XY',
    COMPANY_NAME => 'XYZ, Inc.',
);
my %fnr_but = (
    COMPANY_CODE => 'PQ',
    COMPANY_NAME => 'PQR, Inc.',
);
my $nameRef = \$fnr{COMPANY_CODE};

show('Original');
changeHashLoop();
show('Loop');
changeHashButton();
show('Button');


sub changeHashButton {
    %fnr = %fnr_but;
}

sub changeHashLoop {
    for my $key (keys %fnr) {
        $fnr{$key} = $fnr_loop{$key};
    }
}

sub show {
    my ($label) = @_;
    my $ccRef = \$fnr{COMPANY_CODE};

    printf "%8s: %s (%s)  FNR:  %s (%s)\n",
        $label, $$nameRef, $nameRef, $$ccRef, $ccRef;
}

##</code><code>##

Original: AB (SCALAR(0x94a554))  FNR:  AB (SCALAR(0x94a554))
    Loop: XY (SCALAR(0x94a554))  FNR:  XY (SCALAR(0x94a554))
  Button: XY (SCALAR(0x94a554))  FNR:  PQ (SCALAR(0x94a584))