#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

my @fields = 'a' .. 'z';
@fields[ 10, 14, 24, 26] = ('1/2/2016') x 4;
$_ = sprintf '%04d-%02d-%02d', (split m:/:)[ 2, 0, 1 ] for @fields[ 10, 14, 24, 26 ];
say join ',', @fields;