if($acctn != $curr_acctn) {
        ...

##</code><code>##

        foreach my $account (@account_list) {
            ...

##</code><code>##

#!/usr/bin/perl

use strict;

( @ARGV == 2 and -f $ARGV[0] )
    or die "Usage:  $0  input.file  output.file\n";

my $outname = pop @ARGV;
open( OUT, ">", $outname ) or die "$outname; $!\n";

my $prev_rec;

while (<>) {
    s/^42/CH /;
    s/\s+$/ LAB\n/;
    if ( ! $prev_rec ) {
        $prev_rec = $_;
        next;
    }
    if (( /4039140\s/ and $prev_rec =~ /4039139\s/ ) or
        ( /4039139\s/ and $prev_rec =~ /4039140\s/ )) {
        s/40391(?:39|40)(?=\s)/4039142/;
        print OUT;
        $prev_rec = '';
    }
    else {
        print OUT $prev_rec;
        $prev_rec = $_;
    }
}
print OUT $prev_rec if ( $prev_rec );