foreach $RegEx (@HeaderGarbage){
  $CHRegex = qr/($RegEx\n)/;
  push @HeaderRegExes, $CHRegex;
}
...
foreach $ErrChar (@HeaderRegExes){
...

##</code><code>##

@HeaderGarbage = ('LD 20',
                  'PT0000 ',
                  ...
                  'CUST ',
                  'DATE ',
                  'PAGE ',
                  'DES  ');
my $reg = join '|', @HeaderGarbage;
my $HeaderRegex = qr/^$reg/;
...
while (my $line = <FILE>) {
  $line =~ s/$HeaderRegex//; # replace matching garbage
  ...

##</code><code>##

use strict;
use Data::Dumper;

my @valid_keys = qw/ TN TYPE CDEN CUST AOM FDN TGAR LDN NCOS
                     SGRP RNPG SCI SSU LNRS XLST SCPW SFLT CAC_MFC
                     CLS CPND_LANG RCO EFD HUNT EHT LHK AST IAPG
                     AACS ITNA DGRP MLWU_LANG DNDR KEY DATE /;

my $valid_keys = join '|', @valid_keys;

my $RECORDS = ParseInputRecord();
print Dumper(\$RECORDS);

sub ParseInputRecord
{
    my (%r, $key, $value);

    while (my $line = <DATA>)
    {
        my ($k, $v) = $line =~ /^($valid_keys|\s+)\s*(.*)$/;

        if (!$k) {
            next if !$key;
            $r{$key} = ParseInputValue($key, $value); # finish previous command
            $key = '';                                # reset buffer
        } elsif (!$key) {
            ($key, $value) = ($k, $v);
        } elsif (substr($k,0,1) eq ' ') {
            $value .= "\n$v";
        } else {
            $r{$key} = ParseInputValue($key, $value);
            ($key, $value) = ($k, $v);                # start next command
        }
    }
    # finish off last command in the buffer
    $r{$key} = ParseInputValue($key, $value);

    return \%r;
}

sub ParseInputValue
{
    my ($key, $value) = @_;

    if ($key eq 'CLS') {
        $value =~ s/\n/ /g;
        # if want to transform to array of commands
        # $value = [ split /\s+/, $value ];
    } elsif ($key eq 'KEY') {
        $value =~ s/\n(\D)/ $1/g;   # merge command lines
        $value =~ s/\s+(\n|$)/$1/g; # eliminate end spaces
    }

    return $value;
}


__DATA__
DES  M3310
TN   004 0 00 04
TYPE 2616
CDEN 8D
CUST 0
AOM  0
FDN  7000
TGAR 1
LDN  NO
NCOS 7
SGRP 0
RNPG 5
SCI  0
SSU  0010
LNRS 16
XLST
SCPW 2257
SFLT NO
CAC_MFC 0
CLS  TLD FBD WTA LPR PUA MTD FNA HTA ADD HFA
     MWA LMPN RMMD SMWD AAD IMD XHD IRD NID OLD VCE DRG1
     POD DSX VMD CMSD CCSA-CSI SWD LNA CNDA
     CFTA SFA MRD DDV CNID CDCA MSID DAPA BFED RCBD
     ICDD CDMD MCTD CLBD AUTU
     GPUA DPUA DNDD CFXA ARHA CLTD ASCD
     ABDA CFHA FICD NAID BUZZ AGRD MOAD
     UDI RCC HBTA AHA IPND DDGA NAMA MIND PRSD NRWD NRCD NROD
     DRDD EXR0
     USRA ULAD RTDD RBDD RBHD PGND OCBD FLXD FTTC MCBN
CPND_LANG ENG
RCO  0
EFD  7000
HUNT 7000
EHT  7000
LHK  0
AST
IAPG 0
AACS NO
ITNA NO
DGRP
MLWU_LANG 0
DNDR 0
KEY  00 MCR 2257 0     MARP
        CPND
          CPND_LANG ROMAN
            NAME Darren Powell
            XPLN 27 
            DISPLAY_FMT FIRST,LAST
     01 MCR 2257 0 
        CPND 
          CPND_LANG ROMAN
            NAME Darren Powell
            XPLN 27 
            DISPLAY_FMT FIRST,LAST
     02 TRN 
     03 CFW 4  7000
     04 AO6 
     05 SCC 0257 
     06 RNP 
     07     
     08     
     09     
     10     
     11     
     12     
     13     
     14     
     15     
DATE 14 JUL 2003