I don't understand this line from your code

It checks the reason for why flock failed instead of assuming it's because the file is already locked.

flock returns error EWOULDBLOCK on unixy systems and error 33 on Windows.

it seems like the file handle ($fh) needs to be a global variable, so I used 'our' instead of 'my'. If I use 'my'

Correct. In my version, the END sub kept it alive.

I'd like to add something like this: use Highlander qw( :verbose );

First, :name traditionally has a meaning already. Dashes are usually used for options. As a bonus, -foo means the same thing as '-foo' even when strict is in use, so less quoting is needed.

Secondly, suppressing the message by default is a bad idea. The option should silent the message when provided.

On to the good stuff,

use Highlander -silent;
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BEGIN {
   require Highlander;
   Highlander->import(-silent);
}
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so you need to create a method called import that looks like

my $opt_silent;

sub import {
    my $class = shift;
    $opt_silent = 0;
    for (@_) {
        if ($_ eq -silent) {
            $opt_silent = 1;
        } else {
            require Carp;
            Carp::carp("Unrecognized symbol $_");
        }
    }
}
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But it won't work. The problem is that the module has already been executed (and the lock obtained) by require before import is called.

But you know what? The option isn't really needed. The message can always be suppressed on the command line by using output redirection.

I'm not planning to upload this to CPAN. It seems too simple to bother.

Yet you had to write it and needed help to do so. You can also credit whoever you want in the docs.