This (untested) code might get you started.

open( FILE, "<filename") or die "Can't open file: $!\n";
my @lines = <FILE>;
close( FILE) or die "Can't close file: $!\n";

my $LastWasZero = 0;
foreach my $line (@lines) {
    chomp $line;
    my ($recType, $rest) = unpack "A2A*", $line;
    if ($recType = "00") {
        if ($lastWasZero) { # two consequative 00 recs
            my ($date,$headerNumber) = unpack "A10A20", $lastWasZero;
            #do delete processing on $headernumber $date...
        }
        my ($date,$headerNumber) = unpack "A10A20", $rest;
        $lastWasZero = $rest;
            next;
    }
    else $lastWasZero = "";
    if ($recType eq "01" ) {
        my ($field1,  $field2,....) = unpack "...", $rest;
        # process 01 records
            next;
    }
    if ($recType eq "02" ) {
        my ($field1,  $field2,....) = unpack "...", $rest;
        # process 02 records
            next;
    }
    ....
}
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Coded for clarity rather than efficiency

Corrected cut&paste error & brain fade error