The safest way to deal with CSV is with a module, and they're easy to use, so there's no reason not to. Let the module cleanly divide up the fields, make the changes you need, and write the results back out to a new file.

#!/usr/bin/env perl
use 5.010; use strict; use warnings;
use Text::CSV;

my $ic = Text::CSV->new({sep_char => ','})                            
+  
        or die Text::CSV->error_diag();
my $oc = Text::CSV->new({sep_char => ',', eol => $/ }) 
        or die Text::CSV->error_diag();

open my $if, '<',  'infile' or die $!;
open my $of, '>', 'outfile' or die $!;

my %states = ( '0H' => 'OHIO',
               '0R' => 'OREGON',
           );

while( my $r = $ic->getline($if)){
    $r->[0] = 'CONDENSED' if $r->[0] eq 'C';
    $r->[0] = 'FINAL'     if $r->[0] eq 'F';
    $r->[4] = $states{$r->[4]} if $states{$r->[4]};
    $oc->print($of, $r);
}
close $if;
close $of;
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