Use substr

#!/usr/bin/perl
use strict;

my $infile  = 'infile.txt';
my $outfile = 'outfile.txt';
open my $in,'<',$infile or die "Could not open $infile : $!";
open my $out,'>',$outfile or die "Could not open $outfile : $!";

while (<$in>){ 
  chomp;
  my $spaces = substr($_,39,5); 
  if ( $spaces eq '     '){
    substr($_,5,5,'');
    $_ .= $spaces;
  }
  print $out "$_\n";
}
close $in;
close $out;
[download]