index + substr: 
my $str   = 'ABCOPCOGNHVCOHL';
my $index = 0;

while (($index = index($str, 'CO', $index)) > -1) {
    substr $str, $index, 2, 'C/O';
}
print "$str\n";

__END__
ABC/OPC/OGNHVC/OHL

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In reply to Re: How to insert a "/" within a string? by trizen
in thread How to insert a "/" within a string? by rsvp1920

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