After thinking further, I suspect I would actually prefer the following:

sub make_expression {
    my ($item, $config) = @_;

    return $config->{prefix} . $item . $config->{suffix};
}

my $formatted_item = make_expression( $item, \%config );
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The thinking is this:

• You have configuration mixed with input in the middle of your code. That's similar to mixing presentation and business logic. Don't do that.
• tye is absolutely correct in that change is the only constant in maintenance. The solution most people use to handle such things is to factor out the piece that can change and give it an unchanging name. That way, you don't care how it happens - it just does.
• This is a really small step away from creating a presentation object that has, as an initialization parameter, configuration. So, that code then becomes:

  my $formatter = Formatter->new( config => \%config );
  
  # many lines and modules later ...
  my $formatted_item = $formatter->format( $item );
  [download]