This is more of an observation rather than answering your question but using alternative delimiters in your substitutions can make the code much easier to read. Also I find that it is easier to use the hex value for a backslash rather than the character itself, e.g. converting to Unix-style paths ...

johngg@aleatico:~$ perl -Mstrict -Mwarnings -E 'say q{};
my( $path ) = qw{ C:\Users\fred\file.txt };
say $path;
$path =~ s{\x5c}{/}g;
say $path;'

C:\Users\fred\file.txt
C:/Users/fred/file.txt
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Going the other way, I would use a lookahead, the chr function and the e modifier in a substitution to do escaping.

johngg@aleatico:~$ perl -Mstrict -Mwarnings -E 'say q{};
my( $path ) = qw{ C:\Users\fred\file.txt };
say $path;
$path =~ s{(?=\x5c)}{ chr 92 }eg;
say $path;'

C:\Users\fred\file.txt
C:\\Users\\fred\\file.txt
[download]

It seems easier to my eyes. I hope this is helpful.