No. There is every need to speculate with your code, Wassercrats. My code was not meant to replace yours, or even reproduce 100% of the functionality. It was to show you that you can do what you are trying to do with much less code! How about this instead: it truncates the string to the first two letters (lowercased) and adds incremented numbers for each collision. And this time i won't require you to use a module!

my (%symbol,@old,@new);

while (<DATA>) {
   chomp($_ = substr lc($_),0,2);
   push @old, $_;
   $symbol{$_}++;
   push @new, $_ . $symbol{$_};
}

print "$_\n" for @new;

__DATA__
Line one
Line two
xxxxxxxxxxx
Another line
xxxxxxxxxxx
Lines end here not
xxxxxxxxxxx
Fourth line (used to be)
Line five
Lines end here
Lines end here too
[download]

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)