When you're on Windows, \n actually means CRLF. So the safest approach is to explicitly split on CRLF

Not exactly. The translation happens during reading/writing. Once you have read your file into memory, \n is \x0A on every platform (otherwise, length("\n") would be 2 on Windoze. So my intention was to suppress the translation on writing, by setting the file handle to binmode.

open my $out, '>:raw', $out_filename

I think I will try this; after all, this is a good occasion to get familiar with IO layers in Perl. If it suppresses \n conversion, the s/// won't be necessary. I'll post my findings.

Still, it would be interesting to know why my binmode() did not worked. Is binmode not supposed to be used in that way, or is there a bug in the IO::File::binmode implementation?