@PRC_PRIV_ONLY = (
  'one string',
  'two strings',
  'three strings',
);
foreach my $element ( @PRC_PRIV_ONLY ) {
  $element .= ' appended data';
}

##</code><code>##

foreach my $element ( @PRC_PRIV_ONLY ) {
  $element = [ $element, '2nd element' ];
}

##</code><code>##

@PRC_PRIV_ONLY = ( 
  [ 'one string',    '2nd element' ],
  [ 'two strings',   '2nd element' ],
  [ 'three strings', '2nd element' ],
);