#!/usr/bin/perl -w
use strict;

## their side before sending the file to you...
my $line = "ABC|John Smith 1234";
my ($groupID, $text) = split(/\|/, $line, 2);
$text =~ tr/a-z/f-za-e/;
$text =~ tr/A-Z/I-ZA-H/;
$text =~ tr/0-9/4-90-3/;
$line = $groupID . "\|" . $text;
print "$line\n";

## And then on your end...
my $myGroup = "ABC";
my ($group, $data) = split(/\|/, $line, 2);
if($group eq $myGroup) {
  $data =~ tr/f-za-e/a-z/;
  $data =~ tr/I-ZA-H/A-Z/;
  $data =~ tr/4-90-3/0-9/;
}
print "$data\n";