#!/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;
# My change is below
$_ = sprintf '%04d-%02d-%02d', (split m:/:)[ 0, 1 ] for @fields[ 10, 14, 24, 26 ];
say join ',', @fields;

__END__
Missing argument in sprintf at tmp.pl line 8.
Missing argument in sprintf at tmp.pl line 8.
Missing argument in sprintf at tmp.pl line 8.
Missing argument in sprintf at tmp.pl line 8.
a,b,c,d,e,f,g,h,i,j,0001-02-00,l,m,n,0001-02-00,p,q,r,s,t,u,v,w,x,0001-02-00,z,0001-02-00