use strict;
use warnings;

use constant GROUPS => {
    A => 1,
    B => 2,
    C => 3
};
GROUPS->{B} = 22;
GROUPS->{D} = 'Not a constant!';
use Data::Dumper;
warn Dumper [GROUPS];
__END__
$VAR1 = [
          {
            'A' => 1,
            'D' => 'Not a constant!',
            'C' => 3,
            'B' => 22
          }
        ];