Works for me if I invoke like this:

rnm "s/Blah Blah - \d{2} - //" "Blah Blah - 01 - Peter.txt" "Blah Blah
+ - 02 - Lois.txt"
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Of course, that requires I supply the names of the files to be renamed because cmd.exe doesn't expand wildcards for you. If you want that to happen, you'll have to modify the script a little:

#!/usr/bin/perl -w

$op = shift or die "Usage: rename expr [files]\n";

chomp( @ARGV );
@ARGV = map glob, @ARGV;

for ( @ARGV ) {
  $was = $_;
  eval $op;
  die $@ if $@;
  rename ( $was, $_ ) unless $was eq $_;
}
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Then rnm "s/Blah Blah - \d{2} - //" *.txt works.